Here’s some links to some online courses to get you started. I think you might have to pay for the second one, but the first one, from Cisco, is free. (You’ll need to create a Cisco account, however.)
It’s absolutely great experience, and I could write a whole screed about what to look up, or I could point you to sources that are better organized than me, so I’m going with the latter.
Here’s a link with many different free Cisco courses: