By doctor prescribed me cerefolin he said it helps for OCD, is that true? Please explain why it would help. Thanks

Maybe. Vitamins in cerefolin, vitamin b12, folic acid are believed to be important in the production of the neurotransmitters serotonin and dopamine. Especially the former. The police says, that's by providing more vitamin b12, it enhance its production of serotonin and that's help with OCD symptoms. It is worth a try.
Cerefolin. This is a drug made of combination of Vitamin B12, Folic acid, Vitamin B2 & Vitamin B6. The form used here is L-methylfolate & is used as an adjunctive therapy for depression.