The first step of DNA replication is unwinding the DNA double helix.
A replication fork is the transition region between paired and unpaired DNA strands.
Since DNA polymerase can assemble DNA only in the 5' to 3' direction, the new strand complementary to the 3' to 5' strand must be assembled in short 5' to 3' segments, which are later joined together by ligase.
The synthesis of a DNA strand begins with the formation of an RNA primer.
An old DNA strand is used as a template for the synthesis of a complementary new strand.