Step 1: While not waiting for the offer letter to come, you can open your online immigration file and pay your respective processing fee ($101). Go here:http://www.immigration-quebec.gouv.qc.ca/en/immigrate-settle/students/obtaining-authorizations/certificat-acceptation/index.html
Step 2: After opening and paying the fees, they will give u a check list that indicates what are the items needed to send to them, it will be a passport size pic (immigration size), your offer letter after u receive it, photocopy of your passport etc.
Step 3: Send it via express courier to them.
Step 4: Wait for few weeks, they will review it and send your CAQ to embassy and give u a letter stating that "your CAQ is ready and sent to embassy, please go and apply there".
Good luck buddy