How about right here?
There are lots of on-line resources right on this site, in other areas (such as the Wiki, or on-line encyclopedia). A huge search
facility where you can discover that almost any question you could ask has been asked, and answered, before.
I suggest that you keep a diary ... a number-two pencil and a spiral notebook ... so that you can write-down what you have done, what questions you have, the answers to those questions. Pace yourself:
a diary enables you to "never forget" the questions you have when they seem to all come in a great big flood.
There's also a lot of on-line documentation that is distributed with any distro, and copies of it are available on the distro web-sites.
Pick a topic and skim
it, at first, writing down other topics that you want to skim in your diary but not
diverting your attention immediately to that topic. Take your time.
There's a lot to know, and you'll never quite finish doing it.