Glycogen synthase participates in the glycogen biosynthetic process along with glycogenin and glycogen branching enzyme. Extends the primer composed of a few glucose units formed by glycogenin by adding new glucose units to it. In this context, glycogen synthase transfers the glycosyl residue from UDP-Glc to the non-reducing end of alpha-1,4-glucan. {ECO:0000269|PubMed:1731614, ECO:0000269|PubMed:9691087}. This is the function of GYS2 (glycogen synthase 2, Ensembl gene identifier ENSG00000111713).