Here's a breakdown:

* RNA polymerase is a complex enzyme that reads the DNA template and uses it to synthesize a complementary RNA strand.

* Elongation is the stage of RNA synthesis where RNA polymerase moves along the DNA template, adding nucleotides to the growing RNA chain.

* Nucleotides are the building blocks of RNA (and DNA). They are added to the RNA chain in a 5' to 3' direction, following the base pairing rules (A with U, G with C).

So, RNA polymerase is the key player in RNA elongation, responsible for assembling the new RNA molecule strand by strand.