The LaTeX Companion was invaluable to me when I first tried learning LaTeX many years ago. You don't have to read it cover to cover, just read the parts you need as you go. I've almost worn my copy out from so much use. All the online documentation and tutorials are fine, but for me this book was the best way to get started.
Find a good book. I have one (I think it's this one: https://www.amazon.com/dp/0201362996/ref=cm_sw_r_taa_ZBGxxbFYM23S2) and the fact it shows you a ton of packages and how to use them fantastic. I haven't come across a tutorial that has remotely as much info as that book.
You are light on specifics. Have you read the <em>fntguide</em>? A perhaps easier doc to start with is <em>Math Font Selection in LaTeX and Unicode</em>. And here is always the Companion.
I started my learning history, when books were still a thing. So I had a version of this book here: Latex Companion. (I think that there might be some existing in your library of choice.)
This took me a long way until I wanted to do something fancier than just writing my thesis. My first exposure to something more fancy was komascript and its manual here: Koma Script
Once you are there you can read through all the packages that interest you on CTAN. One recommendation from my part and a particularly extensive documentation is the graphics package tikz/pgf: TiKz. The manual has more than 1272 pages, which should allow you to learn everything.(About that one package anyway.)
The LaTeX Companion and/or the Guide to LaTeX are probably the most comprehensive, definitive guides out there. However, for getting started, I'd second/third/whatever the recommendations for The Not So Short Guide to Latex2e (aka lshort.pdf).
I would also suggest that you use XeLaTeX rather than plain-jane LaTeX. It adds nice features like easy support for Unicode and OpenType fonts. You can read up on it in the XeTeX Companion.
Edit: incidentally, when you're writing TeX or LaTeX in plain text, capitalize it thus. ;-)