I furnished most of my apartment from Ikea
. The stuff is easy to put together and doesn't require a particularly large brain pan. Granted some of the stuff is easier if there are 2 sets of hands working on it, but it's really straightforward stuff so long as you follow the clear, set-by-step instructions.
By and large you get everything you need in the pack. Having said that, for a lot of the goods you'll need to have a Philips-head screw-driver which you can pick up in absolutely any hardware store. Also, for bigger items such as wardrobes it never hurts to have a hammer handy for uncooperative joints. Put a blanket (or the packaging) down on the floor to protect the parts and away you go.
If parts are missing or damaged then you can simply return the goods and get a replacement. If they delivered it then they will pick it up again, otherwise you have to go back to the shop.