Once you have the physical certificate or the e-certificate, you can literally go the same day to a passport office* and apply. (Note that most people will not want to mail the physical certificate although they do return it).
So your next steps are: download the application form, get your photos, start filling it out in advance even.
*Note that although they're technically part of Service Canada, there are some 'passport office' locations that provide full service i.e. accept in-person passport applications. 'Regular' Service Canada locations basically only help you fill out the passport application and do some checking and then forward it to the passport agency, more or less same as by mail. (Checking is very useful, mind.)
This sounds more complicated than it is (historical reasons that the passport agency and service canada used to be completely separate); but just check in advance to see what level of service is available at each location:
https://ircc.canada.ca/english/passport/map/map.asp