You will need your 14-digit VOCaL library card number and insert "Ontario Library Service- North" as your library name to access this service.
The Toronto Public Library has posted good tip sheets to help you use OverDrive:
Getting Started Guides
http://www.torontopubliclibrary.ca/books-video-music/downloads-ebooks/ebooks-userguides.jsp
OverDrive FAQs
http://www.torontopubliclibrary.ca/books-video-music/downloads-ebooks/ebooks-faq.jsp
OverDrive Troubleshooting
http://www.torontopubliclibrary.ca/books-video-music/downloads-ebooks/ebooks-troubleshooting.jsp