new puppy - flea treatment

I have inheirited a 4-month old beagle puppy from a great niece. She bought it but soon lost her apartment. I got his shots the other day but hadn't had a pet in awhile and was shocked at prices. So I didn't get his flea treatment yet and am taking him back June 4.
In the meantime, I have 3 question.
1. The vet mentioned a cream or salve that is applied to the back of the neck to keep fleas away (or does it kill them)? What is this stuff?
2. Do I have to take the puppy in for a flea treatment each time he needs it or can I apply this stuff myself?
3. What can I do now? The flea collar doesn't appear to do much good and the vet doesn't approve of them anyway.