This will tell you how to use some rudimentary joinery techniques:
Making basic cuts, mitres, and chopping out joints.
It's aimed at complete novices, so if you already have any knowledge of woodwork some or all of this will likely come across as patronising. Sorry about that.
Sawing a piece of wood is a really easy job, but without a little training most people screw it up. Going straight through quickly is a good way to end up with non-square joints, and when you're making furniture they're a very good way to make it look terrible.
My first ever job was as a joiner's apprentice, and because I didn't enjoy it I sucked. 11 years later I find myself making basic furniture. Remembering all the advice I was given, taking my time, and doing something I want to with it, I find I don't suck so badly: Doing passable joinery only takes a little knowledge coupled with care and attention.
One important technique that doesn't need much showing: Pilot holes
When you drive a screw or hammer a nail into a small piece of wood or too close to the edge of one, it will split. Sometimes putting a fixing into a place like this is unavoidable. Drilling a hole through the joint a little bit smaller than your fixing will prevent it from splitting.
Step 1: Tools
You don't need fancy tools to make good woodwork. You could buy a very expensive set of Japanese chisels for woodcarving, but it won't matter if you're an awful carver and don't know what you're doing.
I'll be keeping this to very basic, cheap tools:
Hardpoint tenon saw
You can be more precise when marking wood with a pencil than a pen, and even heavy pencil marks are easier to sand off than greasy biro. Use light pencil marks ;)
A hardpoint tenon saw, unlike a proper one, has to be thrown away once it becomes blunt because it can't be sharpened. However, if you only seldom make joints, it's all you'll need and very cheap. I think the expense and maintenance of a good tenon saw is only worthwhile if you're going to actually use it a lot.
The square you see in some of these photos is an old, cast iron Rabone one. I don't think you can get them like that any more, but there's plenty similar available.
Pump cramps are one of the best tools I've found: Inexpensive, very quick to apply and remove, and two are secure enough to hold most work pieces in place. Put cardboard between the cramps and your workpiece, because sanding or planing the marks out later is really annoying (see pics 3 and 4).
As you can see below, I've improvised a workbench from an old chest of drawers. Be careful not to hurt your back if you do this (or use a workmate type thing), a proper workbench is a good deal higher for this reason.
Step 2: Basic Right Angled Cuts.
When marking wood, the same as when doing any kind of geometry by hand, it's easy but mistaken to view the marks you're making as mathematical abstractions; just as a dot can be thought of as a point with no dimensions but in fact just represents it, so too it's easy to think of the lines you make on wood to represent cuts as having no width. This is a first step toward making bad cuts, and over the entirety of a piece of furniture, a millimetre here and there all adds up to something visibly wonky.
You have to be conscious of the width of your lines and the width of your sawblade to cut precisely. I also use arrow marks to indicate which side of the line to cut on.
Also, when marking, don't go around the sides in sequence, because there's a good chance your last line won't quite line up when it meets the first one you made. Instead mark one side, then one adjacent one going from the marked corner down, then the other adjacent one in the same way. This allows you to get all three as uniform as possible. You don't really need a line on the underside.
To start the cut, position your saw on one corner of the markings and draw it gently backward to make a notch. You can rest one thumb one the top of the wood and the side of the blade to keep it aligned. Repeat to make the notch deeper, then gradually flatten the saw off and start working it forwards and backwards to make a shallow cut all the way along the top line.
Don't push down on the saw at any point while cutting or it will stick; just work it backwards and forwards and the saw teeth will go through the wood easily.
Now you've got the top cut shown in image 2, it's tempting to quickly saw all the way through. If you do it this carelessly, the saw will wander all over the place either side of the other lines, then also splinter the bottom as it goes through.
You have to cut squarely along *all* of your lines to actually get a square end, so working in the groove you've made, tilt the saw and work a similar groove into two of the other lines you've marked one at a time.
You've now got three grooves that will keep your blade straight as you saw through the wood left in the centre (pic 3). You can go through this quite fast now, but slow down near the end so as not to ruin the surface underneath. I find it best to work with the saw tilted right back at this point to slowly cut through the last bit, this minimises splintering.
Step 3: Hand Cut Mitres
Mitres are very easy to screw up. They're certainly much easier if you have a proper mitre saw or chopsaw, but those tools are fairly expensive and take up a lot of space. If you're careful, you can manage perfectly acceptable mitre joints with hand tools.
I'm using the example of a 45 degree mitre here because it's more commonly needed and much more straightforward than odder angles, in that a square is already set up to quickly mark 90 and 45 degrees.
So, working from the corners of a square ended piece of wood, mark your 45 degree lines and join them with a 90 degree one. Bear in mind that only the 45 degree lines will really tell you exactly where to cut, the 90 degree line will just help you make sure you're cutting straight between the 45 degree ones. It's unlikely that it will align perfectly with where the cut needs to be. However, the corner of the piece of wood will reliably tell you if you're cutting straight down or not.
Just like with your thumb on a square cut, use a couple of fingers to keep the saw blade aligned on the top 45 degree line while cutting the first groove.
Once the first part of the cut is in place, work the saw carefully down the back at the corner (pic 4). Then run it down the front, parallel to the 90 degree line. Take care, cut slowly, and you'll get a near perfect 45 degree cut.
Mitre joints are not absolutely necessary to join pieces of wood at right angles, but they're certainly a lot prettier than just butting pieces up to each other.
Step 4: Chopping Out Joints
There's an absolutely bewildering array of joints that can be cut into wood, some taking a great deal of skill to set up correctly. I'm just going to show you the most basic skills to cut one piece of wood to fit around another.
Pic 1: First, you need to mark out exactly what you're going to chop out of the piece of wood. I'm cutting this length of 40 x 40mm wood to fit around something measuring 25 x 50mm. It helps to shade it out too becasue that way no matter how many time you turn the wood around, you can always quickly see what's going to be cut out.
Pics 2 and 3: Start just like with the other joints, cutting a small groove on either side of the block to remove, keeping things square and working down as far as you need to. Then make more parallel cuts throughout the block to split it into lots of smaller blocks.
Pics 4 and 5: Now use a mallet and chisel to indent down the line at the bottom of the blocks you've cut into it. They're going to be knocked out in a minute, and this line makes sure that they won't take wood with them that should be left intact. Indent the line on both sides!
Pics 6 and 7: Now put your chisel in the line and gently tap it into the wood to split blocks off. Keep going until you end up with something like in pic 7.
Pics 8 - 10: This won't quite fit, so it needs to be made concave. From slightly forward of the edges, work slowly in and down with the chisel and the excess will come up as strips like in pic 8. Cut these out by going down into the ends of them like in pic 9, and repeat until you end up with a concave joint like in pic 10.
That's it. As you can see in pictures 11, 12 and 13, it fit's adequately though not perfectly.
Step 5: Conclusion
This instructable was the first time I've done joinery in a decade, and I sucked way more back then than I do now. That's just because I was impatient before.
The *basics* of joinery are about common sense and method rather than high levels of skill and obscure knowledge (though they certainly come into play when, say, making foxtail wedges: joints where a peg splays around wedges as it's pushed into a socket, locking it firmly into place without glue or fixings).
These basic techniques can be combined to construct a lot of things out of wood. No matter how awful you think you are at joinery, as long as you're careful and patient you can produce passable woodwork.