PCR amplifies a specific gene from essentially a signal copy of DNA.
Essentially, the are THREE steps in the PCR cycle.... 1. Denaturation 2. Annealing of the Primers and Polymerases and 3. Extension/Elongation
1. Denatureation (Seperation of the the DNA strands) is needed when you have double stranded DNA. It is usually done at 94C, for 20-30 seconds.
2. Annealing is when you have to attache your primers and your polymerase to the DNA strand. Usually this done at 54C for 20-40 seconds
3. Elongation is when you continually add bases following the primers until you fully synthesize a new strand of DNA. This is done at 72C for about 2 minutes (or longer, depending on how long the gene of interest is).
These are the basic steps, however, the is a Step before (called the Intialization step) and a step at the end of the process (called the Final Elongation step)
The best source to look up PCR for general information is on Wikipedia. So... try that.
If you want to know anything specific, like how you create the primers, or where the primers are placed in accordance to which gene you which to amplify, you can message me
Hope this helps...