You share the workload with the billing department. It's sort of difficult to describe because you're pretty much doing something new everyday. During my time there we had to know how to do a variety of tasks, I'm pretty sure my notes covered over 30. The most important tasks involved drafting and finalizing invoices and creating records based off some sort of contract. It wasn't difficult per say, but you have to have attention to detail and a patience for this kind of stuff. It's literally a 12-16 step process to create a record, enter everything in Elite (an accounting software they use), and draft and finalize invoices. If you mess up on one of the steps, it may take 2 or so hours to fix, or if you cc the wrong person on an invoice, someone who isn't supposed to be privy to that kind of information might find it in their inbox.
The day-to-day looks something like this: A client requests a task for completion, the manager forwards it to you, and then you complete and follow up with the manager afterwards before a designated time. I personally terminated my contract with Analysis Group prematurely because I wanted to try out other opportunities, but they were eventually going to have me manage two of their major clients all by myself. The part where the client contacts my manager would be basically skipped. I'd also be responsible for other requests as well, like if someone was getting way more than they could handle at the end of the month, the team would help him/her out, but my main responsibility would be to handle the assigned clients.