What does the job or MOS "Legal" mean to a new Marine recruit?

Desk jockey. You’ll be admin. You’ll copy/paste new names into courts martial and NJP packages, type the cover sheet and submit to the Adjunant officer for signature. It’s a pretty skate job, but not exactly what anyone was imagining when they joined to be a "MARINE" I got stuck in the legal office for two months once because of my previous civilian employment (you don’t have to be admin to get stuck in an admin job). If I’d wanted to work in an office, I would have stayed civilian and made better money and dealt with less military bs. It’s not bad, but you’ll never do much that is interesting. It took a lot more connections than it should have to get me out of there.
–And does that mean you’ll have legal experience in the civilian world?? Nope. You’ll have administrative assistant skills. That pays $9/hr.

It sounds as if their Military Occupational Specialty will be working in the legal office as a military equivilent of a paralegal specialist. Helping out military lawers (JAG) judge advocate general, with cases, and paperwork and such. Probably looks real good on a resume when the person leaves the military service to get a job with at a lawyers office, or working in local government.

It means their job title is in the "Legal Department" within the Marine Corps. He may be a clerk which is like an administrative job, or it could also be someone who record, researches, or finds out about Directives,Rules, regulations or other things.