as the previous commenter said, it depends on the programs but i can give you an idea of how it's been for me so far!

on the ouac, i basically filled out all my information, uploaded any required documents and i chose my three programs. i submitted everything on sunday and i was given an ouac reference number and told that i would have to wait around 2-5 business days while they processed my application and payment. during those days, i wouldn't be able to make changes to my applications. surprisingly, it finished processing on monday. after that, im basically waiting for the universities to email me back telling me they got my application + additional info.

as for supplementals, i applied to waterloo which requires/recommends?? applicants to fill out an AIF. i wasn't given the AIF while choosing programs on the OUAC- instead, waterloo emailed me today telling me that they received my application and gave me instructions to create an account on their website. once i created the account, i was able to access and fill out the AIF. obviously this process won't be 100% identical with every other school but i would imagine that it's similar??