DNA can be likened to a zipper. As with a zipper, the two DNA strands are connected by hydrogen bonds formed between nucleotides. When replication occurs, the twisting of the strands unravels, akin to opening a zipper. The strands separate, just as the teeth of a zipper do when it is unzipped. Each strand is capable of generating a new strand.
However, just like improper handling or wear can damage a zipper, DNA replication can also introduce errors that may result in mutations.