The way it works is you log onto UPSers and file a request for reimbursement. After the semester is over, you will receive a check for the amount that was accepted, as long as you pass all your classes. You are eligible immediately and the coverage is pro-rated, so even if you start working part way through the semester you are good. I can't exactly remember how to create username, password, etc. for UPSers.com, so that will be a question for your boss/HR person.
I wouldn't recommend taking more than three classes!