Heat shrink tubing, is as the name implies, a tube, that shrinks when heated, it's used in our applications for insulating the bare joints made between wires, and connections to appliances, you don't want the exposed portions of the wire to touch places it shouldn't, like the metal body of the van, and thus short out, so you need to insulate the exposed areas of conductor you stripped to make the connection, it's used more when joining 2 or more wires together that are going to be part of a wiring loom, but it can be used anywhere a join is made between wires, and/or components.

It's sold in different diameters, and some times you can get different shrinkage characteristics,  remember that the diameter it is when unshrunk, is at least double what it will be when shrunk, you want it so fit over the wires your using easily, and shrink to smaller than the diameter of the wire for a good seal.

This is how much larger the tubing is compared to the wire I'm going to be shrinking it onto (this is about 10 amp wire here, and the smaller tube shown in the picture to the left).

This is fine, as you can use this tube for double wire splices etc.

This is far enough for normal 10 amp wire, but the thicker the wire, the longer you'll have the iron on the conductor to heat it up for the solder can flow, so move the tube as far down the wire as possible.

You can see in this picture, the tube is longer than the join, that's what you want, the tube will shrink in length slightly, but you want the tube to shrink tightly over the insulation of the wire as well as the bared conductor, restoring the insulation properties as if there was no join there.

Then you shrink the tube onto the wire join, as the name implies, you use heat to shrink it, ideally a hot air gun, that's where the hot air blower attachment that comes with the gascat gas powered soldering irons comes into it's own), but you could use a hair dryer, a fan heater as I'm doing here,

Or even if your careful, use the body of the soldering irons bit (not the end with solder on it), gently brush the hot bit over the tube to shrink it, even heat from a lighter can be used, but is not recommended, (you need above 90 °C to shrink most tube, it wont burn if you get it too hot, but the pvc insulation on the wire will bubble, smoulder and melt if your not careful with direct heat).

And this is the finished join heat shrunk join.

as the heat shrink tube shrinks more than the diameter of the wire, it will grip tightly over the actual connection, hence you can see the outline of the solder join here, it looks a lot neater than electrical tape, (which always peels off after a few months, and looks even worse), and if you ever need to get to the actual join under the tube, you can slice it off with a sharp knife, if the wire is going to be exposed to the weather, this is usually enough, but if it's going to be driving rain, or be submerged in water, then use the heat shrink with the adhesive lining, that stuff is permanent, you are better off chopping the whole join out of the wire if you need to disturb a join covered with the adhesive heat shrink.

 (actually, nowadays liquid electrical tape can be good, it's a brush on rubber liquid, that sets over the join, but can be a bugger to get off if ever needed),
Insulation tape is sold in many different colours, widths, lengths and qualities, the cheaper stuff (pound shop and market stall variety) is not nice to use at all, it is very inflexible, in cold weather it's almost impossible to use, and the adhesive leaves a lot to be desired, decent quality insulation tape can be stretched around the join, and that helps bond it to the join, (cheap stuff snaps before you can stretch it enough), make sure you use proper electrical insulation tape tho, as it's designed to mimic the  insulation on wires, and thus remains electrically insulating upto very high voltages (about 9Killo volts), and can take high temperatures, sellotape and masking tape will break down at high voltages if used for insulating bare conductors, and can catch fire if the wire heats up for any reason.

You can also get what's called self amalgamating tape, this is an insulation tape for use where it is imperative that moisture never gets in the joint (the connection to a satellite dish uses this tape, as water in that joint will bugger things up very quickly.. water can wick up coax cable, and you'll end up with rusted wires, shorted components, and eventually the water will reach the equipment inside the house.. not good), the self amalgamating tape has 2 sticky sides, one more sticky than the other, you cut off a length of tape, peel back the backing, and wrap it round the join, you have to stretch the tape to at least double it's length as you wrap it around the joint, this causes the tape to actually melt into it's self, creating a water tight joint that'll last forever, use this tape only where you really need it, i.e. outside the van, as it's not cheap, and is a bit of a faff around to use.

Here's some good quality insulation tape, a 2 inch strip has been unwound from the reel, shown here.

And here's that same 2 inch length, being stretched.

Here's me wrapping a spliced crimp connector join with tape.. this is red stuff, I use to identify positive connections on wires that aren't red already,

And to stop the insulating tape coming undone in a years time if the wire is exposed to moisture, I touch the body of the soldering irons bit on the tape, where the end of it  has been overlapped back over the tape already there.

This melts the end of the tape into the rest of the tape, preventing it from unwrapping it's self later (poor mans heat shrink :)