You must contact a recruiter in order to join the United States Coast Guard. You need to be physically fit and between 17 and 27 years old. You also need to be able to meet the mental and character standards they have set.
No, signing up for the Coast Guard, both Active duty and reserves is just like anyother military service, and "they" pay you. If you're interested in a non commital Coast Guard type job, there's always the Coast Guard Auxilary. Try going to their site at cgaux (dot) org.