What is DNA polymerase?
DNA Polymerase is the enzyme that catalyses the formation of bonds between complementary DNA base pairs, and hence the process of DNA Replication.
During replication, after the strand is unzipped, the polymerase runs over the strand, adding complementary base pairs and forming a complementary strand.
It operates only in the 5' to 3' direction, which presents issues in the synthesis of the lagging strand of the DNA.
That's a basic overview of what it does. Hope that helped :)