PCR is a technique that amplifies a specific region of DNA between two known DNA sequences using primers, DNA polymerase, and thermal cycling. The key components needed for PCR are a buffer, magnesium ions, dNTPs, DNA polymerase enzyme, primers, a DNA or RNA template, and water. The process involves denaturing the DNA template, annealing primers to the single-stranded DNA, and extending the primers with DNA polymerase to make copies of the DNA region between the primers. This allows for exponential amplification of the target DNA sequence.