I'm not 100% sure whether you're referring to extending your current visit permit or whether you're referring to applying for the outland permanent residency but here's the information for both:
Extension of a Current Visit Permit
http://www.cic.gc.ca/english/visit/extend/visa.asp
I would suggest applying online if you can as you'll have implied status from the moment you send the application as long as your current visit permit is still valid at the time. The fee is $100. You'll need proof of funds (I sent bank statements for my joint savings account and a few months of pay-stubs as I was moving from a WP to a VP.
Applying for Permanent Residence Outland
http://www.cic.gc.ca/english/information/applications/fc.asp
Although you might want to start looking at the information now - I'd suggest not filling in the forms right now as they get updated from time to time. I would download them about a week or so before you're ready to send just to be safe. Now IS a good time to start thinking about your evidence and gathering it etc.
As mentioned on here a few times - remember, you are NOT in a common-law relationship until you hit that twelve month milestone. When a form asks you which date you entered into a common-law relationship, it is the date AFTER WHICH you had been living together a year.
Good luck!