At OCS, you will have a variety of staff and instructors from many ranks and MOS.
OCS is organized as a Battalion, and a Battalion is made up of companies. Then, companies are made up of platoons.
OCS is, in general, organized as such:
At the Battalion Level:
OCS Commanding Officer (Colonel)
He or she is the head of OCS and oversees a battalion, which is made up of companies. When I went to OCS, our battalion had two companies, Charlie and Delta. I was in Delta.
Sergeant Major (I need to look into this. I'm not sure if there is a Sgt Major for each company, or one overall. We had one in our barracks building)
Then each company has its own rank structure, and while at OCS, you will have billets that correspond to each personnel member. These are:
Company Commanding Officer (Major)
Company 1st Sergeant (1st Sergeant)
Company Executive Officer (Captain)
(in the fleet, people nickname this "Company XO." Do NOT do this at OCS)
Company Gunnery Sergeant (usually a Gunnery Sergeant, but you may see a Staff Sergeant acting out of rank)
Within each company are platoons. My company had three platoons. Platoon rank structure is:
Platoon Commander (Captain)
Platoon Sergeant (Gunnery Sergeant or Staff Sergeant)
(All the enlisted staff in my platoon were Gunnery Sergeants. The other platoons had both Staff Sergeants as well)
In addition, each platoon had two additional platoon instructors. They are called:
Sergeant Instructors
At OCS, you will be assigned to a platoon. Each platoon is split into three squads. The Platoon Sergeant and the Sergeant Instructors split the squads to evaluate you, but the Sergeant Instructors are NEVER called squad leaders. You however, may fill a squad leader billet.
So, the billets you may hold at OCS are:
Company Commander
Company 1st Sergeant
Company Executive Officer
Company Gunnery Sergeant
Platoon Commander
Platoon Sergeant
Platoon Guide (works closely with Platoon Sergeant, does not have a staff equivalent)
Squad Leader (this is an awesome first billet to have. It was my first billet and a good introduction billet)
Now to make things even more complicated, each squad is split into Fire Teams. At OCS, your squad leader will pick out their fire team leaders. This is not an evaluated billet, but you are responsible for accountability .
I'll explain more about billets in the leadership section.