PCR has two requirements: single-strand DNA template and a primer with a 3' -OH group.
First, begin with a solution that includes the target DNA, DNA polymerase, dNTP, primers, and magnesium ions in vitro.
Heat the solution to between 90 and 100 degrees Celsius, for about 1 minute, to break hydrogen bonds and produce two single-stranded templates. Quickly cool the solution to between 45 and 65 degrees Celsius, which allows primers to attach to template strands.
Heat solution to between 65 and 75 degrees Celsius, which Taq polymerase functions, replicating the region, and the entire process is able to be done in an in-vitro system, resulting in up to million of copies (clones) from a single DNA template target.