Then one strand of DNA serves as a template for?

If the DNA is in the process of replication, then a single DNA strand will serve as a template for a new complementary DNA strand to form one of two new double-stranded DNA molecules. If DNA is in the process of transcription, then the single DNA strand will serve as a template for a complementary strand of RNA. The new RNA strand will remain a single strand, it will leave the nucleus and go to a Ribosome where it will be translated into an amino acid sequence.