PCR is a method for amplifying DNA that allows one molecule to be increased to thousands within hours using DNA polymerase and building blocks. It has many roles including forensic applications, infectious disease diagnosis, medical applications, and research. PCR can fail due to contamination, so techniques have been developed for optimization including dedicating lab areas to pre- and post-PCR handling, adding reagents to minimize DNA folding, determining the optimal magnesium concentration as a polymerase co-factor, and using measures like disposable equipment and thorough cleaning to prevent contamination.