I totally agree with Jay - you have to be careful here - But if you want to do it ...
Get a short book on basic wiring from the library and read it thoroughly - you need to understand the conventions used and the potential dangers.
The "TAB" - on the side of the outlet, where you attach the wires to the screw terminals - there are two screws on each side of the outlet. On the side with the black wire, you need to snip the metal between the two screws. This effectively creates two separate outlets. Wire one as a switched outlet and one as an unswitched outlet - this is hard to explain - go to a good hardware store and ask for help - it's really pretty simple.
Again - you could electrocute yourself or burn the house down - make sure you understand how the flow of electricity works. Get a knowledgeable neighbor to take a look.