My dentist said i have a hole in my tooth and i should put a little toothpaste on it each night. is there any other way to help seal up the cavity?

Get filling done: The best thing for you to do is to get the decay removed and restored.

Preventive resin: You probably have "incipient" or enamel caries. Placing fluoride, the active ingredient in toothpaste can re-mineralize the area, stopping or slowing the progression of the cavity. You could also have a preventive resin placed - more protective than a dental sealant... It involves abrading the area with a laser, air abrasion or microbur, and sealing the area, which is also very effective.

Yes: Any time you have a hole, you need to get it filled, tooth paste does not work if it is deep groove, they can place sealant if it is decay you need to do a filling, depends on the size.