Bottom line
This section lays out how Marines and civilians become Reserve officers. Most Reserve officers come over from the active component after their AC obligation. The rest come in through the Reserve Officer Commissioning Program (ROCP), which has three tracks (one for AC/AR enlisted Marines, one for SMCR enlisted Marines, one for civilians and prior-service officers). It also covers the Simultaneous Membership Program (SMP), the Platoon Leaders Class (PLC), and how prior-service officers affiliate. If you commission through one of these, expect an 8-year military service obligation (MSO).
What it means for you
If you are enlisted in an SMCR unit, the AC, or the AR and you want to commission, ROCP is your path: get nominated or apply, hit the education bar, then go to Officer Candidate School (OCS), The Basic School (TBS), and an MOS school before reporting to your unit as an officer. If you are a civilian or already an officer in another Service, you come in through an Officer Selection Officer (OSO). If you are a prior-service officer affiliating with the SMCR, Marine Corps Recruiting Command (MCRC) handles your screening and your unit gives you a welcome orientation in your first 30 days.