Installing CDN Tax Receipts For Us
Welcome to CiviCRM! CDN TaxReceipts can be installed through your manage Extensions screen: 

https://docs.civicrm.org/user/en/latest/introduction/extensions/#installing-extensions

If you run into config/support issues you can reach out here on SE. Best to ask detailed questions with screenshots.

If you run into a technical issue you can create an issue here:
https://github.com/jake-mw/CDNTaxReceipts

A number of Canadian IT companies monitor this GitHub repo (Coop Symbiotic, Mustardseed NonProfit, PeaceWorks and ourselves).