Welcome to the forums.
The best way to learn is to actually get your feet wet somehow. This is the hardest part: Look for a Linux distro, to download its ISO. Begin with the page on this site, on the line near the top which says "Download Linux". (Surrounded by "Members" and "Newsletter".) Choose one of those distros and download the ISO. Get a 16GB or 32GB pluggable USB disk that doesn't have anything important on it! Then "burn" the ISO onto the USB. If you don't know how to "burn" then start another topic and ask about it.
Just choose one distro. If you can't decide then you need to look around in Internet search to see what other people are saying. Or maybe on this forum. I'm not going to suggest one or the other, that's up to you.
This is going to be a crash to some people: you should spend a good deal of time on the terminal. Try out some things like creating a file. Like using "FOR" command to repeat an operation for a list of files. Trying to write your first "bash" script and get it to work. It could be fun... but scripting could be a genuine headache because the terminal interpreter is very specific about things, stuff needs to be in an exact place or it refuses to budge. :/ But don't be discouraged by my statements about it. Dealing with the terminal is one of the most important aspects of being a Linux power user. Some people use Linux and rarely deal with the terminal, but that's considered OK these days. But it could be an advantage for you if you could learn it.
Reading books and watching other people doing it on Youtube isn't going to do anything, perhaps except increase suspicion and/or increase fear of making a mistake. If you are serious about getting a certification, you must get your hands on actually using the target product. There is no better way.