In simple terms that can be understood, what exactly does requip (ropinirole) do to the brain?

Dopamine agonist. Dopamine is a major neurotransmitter in the basal ganglia of the brain, and is classified as an inhibitory chemical. Requip (ropinirole) and similar drugs in the class can act as an artificial Dopamine source and promote function in Dopamine circuits, but it does not actually increase the CNS levels, rather it substitutes.