This took me forever to find out so here.
1. Get accepted. Send in your deposit.
2. Set up "New Student Accounts". There is a link on the orientation site. It takes about one week after you send in the deposit for you to be able to actually make your account.
3. Log into one.drexel.edu.
4. Click on "students"
5. Click on "housing" - log in.
6. Fill out the application for Graduate Housing - Stiles (there is no room left in the fancy official graduate housing). Submit it.
7. Log into billpay on the one.drexel.edu site.
8. Click "Deposit", "Housing Deposit", pay the 200$.
9. Wait for your assignment. Still room left in Stiles. I just got my assignment - 206B apparently.
Hope this helps.