Multiple entry visa

[immihelp]

1. My son obtained one year B-2 visa issued from the US embassy in Bulgaria, adjusted to six months stay at the US boarder. Is he allowed for multiple entries in the US without applying for a new visa within one year tourist stay?
2. If he is enrolled in a Master Degree program of study, can he travel out of the country for a vacation? Does he need a travel permit?
I would greatly appreciate your answers.
Sincerely,

[immihelp]

1. Yes.
2.
A- Yes.
B-No.