How to connect all site libraries to cdn?

Question

CDN

Hello, I checked my site through gtmetrix.com
As a result, it says that libraries need to be connected via cdn, compress pictures that are already compressed.
I tried cloudflare, but apparently too stupid, I didn’t understand how to create virtual machines and the rest. Maybe there is a service that is simple, where I could upload libraries and remotely connect to the site.
Or maybe someone has an article on the complete optimization of the site step by step?
How to cache on the server, how to tell the browser to cache.
Site on opencart 2.1