𝐌𝐄𝐃-𝐉𝐀𝐂𝐊𝐒
Basically doctors. They treat any kind of injury, from a paper cut to getting stung by a Griever. The Keeper of the Med-Jacks is Clint and his only mentioned 'employee' is Jeff.

𝐒𝐋𝐈𝐂𝐄𝐑𝐒
Slicers make sure the Glade is provided of meat. They slaughter in the Blood House. A tiny barn is next to it, and that's where they raise the cattle. Winston is the Keeper and it is not particularly mentioned that there are any other Slicers (I think).

𝐑𝐔𝐍𝐍𝐄𝐑𝐒
Seems pretty obvious to me; Runners run the Maze every day. The Doors close and open at six, so they have a tiring day. I imagine Frypan getting their backpacks ready (lunch, water, weapons, medical stuff, compass, etc) every morning, as he is also up early. The Keeper of the Runners is Minho. After running, they map the Maze in the Map Room (I will come back to this).

𝐓𝐑𝐀𝐂𝐊-𝐇𝐎𝐄𝐒
Track-Hoes basically do everything related to gardening (well, maybe not everything... but I'll get back to this later as well). They provide the Glade of anything that can be grown, but also help the Med-Jacks create medicine. The Keeper is Zart.

𝐁𝐔𝐈𝐋𝐃𝐄𝐑𝐒
Builders build everything. Their work is rather sloppy, but they're an important part of the Glade. (Movie) Newt says they don't have a lot going on up stairs, so not all of them are extremely smart. The Keeper of the Builders is Gally.

𝐂𝐎𝐎𝐊𝐒
The Cooks prepare all the meals. They use the food they got from the Slicers/Track-Hoes. Later on, they also serve this food to the Gladers. Breakfast, lunch, dinner. Frypan is the Keeper.

𝐅𝐈𝐑𝐒𝐓-𝐈𝐍-𝐂𝐎𝐌𝐌𝐀𝐍𝐃
The First-In-Command is basically the leader of the Glade. Though they have a rather democratic system, the First-In-Command will make all decisions. Alby has this role.

𝐒𝐄𝐂𝐎𝐍𝐃-𝐈𝐍-𝐂𝐎𝐌𝐌𝐀𝐍𝐃
The Second-In-Command will take lead if something happens to the First-In-Command. If the real leader is dead, the Second-In-Command will become the First-In-Command. If the real leader is hurt, the Second-In-Command is just a temporary leader. The Second-In-Command keeps themself busy with helping around. Newt is the Second-In-Command.

𝐁𝐑𝐈𝐂𝐊𝐍𝐈𝐂𝐊𝐒
Bricknicks are kind of like Builders, except they repair stuff.

𝐒𝐋𝐎𝐏𝐏𝐄𝐑𝐒
Being a Slopper is rather embarrassing. It's the job for those who are not good at any of the jobs listed above. The Keeper is not mentioned, but we do know that Chuck is a Slopper. They wash the dishes, do the laundry, etc. Everything that no one else wants to do.

optional jobs to add (they are in the books, but have a small role. The movies don't show these jobs at all. You could consider combining them with other jobs):

𝐆𝐀𝐑𝐃𝐄𝐍𝐄𝐑𝐒
Gardeners to the easy work in the garden. They plant seeds and make sure they're healthy before giving them to the Cooks.

𝐁𝐀𝐆𝐆𝐄𝐑𝐒
Baggers bury/take care of dead bodies and tend to act like guards. Billy is the Keeper.

𝐌𝐀𝐏-𝐌𝐀𝐊𝐄𝐑𝐒
Map-Makers are related to the Runners. They spend their days studying maps while the Runners run and also help make these maps.

How earning a job in the Glade works:

When you're the Greenie, and you've been given a tour around the Glade, you will start your job trials. The first tryout is always with the Slicers: Newt confirmed this in the books. You can decide the rest of the order for yourself.

During these tryouts, the Greenie will help around with daily things. In the end, the Keepers have a Gathering and discuss what the Greenie was best at. That best thing will become their job and they don't really have a say in the decision.

My tips:

— It's totally fine to make your OC a Runner, but know that it is horribly overused and that readers might become uninterested because of that.

— Obviously you're allowed to create new jobs. Just play around. For example, one of my OCs is a Tool-Maker. 

— Slackers aren't appreciated in the Glade. Unless it fits your story, don't just make your OC hang around and do nothing all day. Alby will scowl at them, lol.