What I want to know about my topic

I would like to know some more things about the Marines. My overarching question is "what is the life of a Marine like?         

• How much do you get a year when you are a sniper?
• How much do you get when you retire after twenty years?
• What if you get injured?
• What are the terms of enlistment?
• How much math knowledge do you need to have?