Military Wives, Tricare Dental?

Sa
My sons going on 2 and my husband who's Navy doesn't know how to go about getting him on Dental, Tricare didn't give him a number or any contact to go about it. They said you can't sign up online like the Tricare Plans so we're kinda at a loss on what to do, any help from anyone who knows would be a big help! Please and Thank You!!