when having a CPU w/out a heat sink, never attempt to turn a computer on.
1. when using a heatsink, you will need some sort of thermal compound. what it does, is it is placed on the CPU and the heatsink goes over it. it transfer the heat of the CPU to the heatsink. Arctic Silver 5 is the best.
2. you need a fan on the heatsink to dissipate the heat, or in other words, get the heat out of the heatsink. If you are not going to overclock, a cheap aluminum fan will do fine.
3. overclocking is when you make you CPU fun at a higher frequency than it is supposed to. thus makes more heat.
4. if you plan to overclock, get a heatsink that is made of copper, copper conducts heat the best and will reduce heat of the CPU.
5. when looking at the specs in a fan, more CFM (cubic feet per minute) is better. it re furs to how much air it moves.
edit--even more info--
6. if you know the socket type/name of your CPU, you know the socket type you are to look for in a heatsink to match and aline with your CPU type.