In protein, synthesis there are two main steps: transcription and translation
In transcription, DNA is copied to mRNA, which carries the information needed for protein synthesis. At the end of transcription, the mRNA molecule leaves the nucleus to match with a ribosome. In transcription, an enzyme called RNA polymerase binds to DNA, unzips the double helix, and uses one strand of DNA as a template to assemble nucleotides in to a complementary RNA strand, while also re-zipping the double helix as it forms the complementary base pairs.
In translation, when mRNA molecule is coded into proteins, tRNA molecule has unpaired bases called anticodons which complement one mRNA codon. Once the tRNA anticodon and mRNA codon match, the tRNA drops off an amino acid and as the tRNA exits the ribosome, the amino acid chain repeats until there is a stop codon.