Helicase unwinds the DNA double helix strucutre
This is done by breaking the hydrogen bonds
Only one strand is then used as a template
RNA nucleotides bond/ attract to exposed bases
This is according with complementary base pairing
The RNA nucleotides are joined to the DNA strand by the enzyme RNA polymerase
Additional: This process results in an mRNA strand called pre-mRNA, which is later spliced to remove introns (non-coding sections of the DNA).