You're going to hate this but it's still as far as i can tell the best way:

  emacs -q
  C-h t RET
  ;; do that stuff
  M-: (info "(emacs")) RET
  ;; read stuff that looks interesting, then:
  q

Then start using emacs:

  emacs <whatever-file>
  ;; don't know what a key does?
  C-h k <that key sequence> RET
  ;; want to add a package? 
  M-x package-install <the package> RET
  ;; don't know what a function is? 
  C-h f <the name> RET
  ;; don't know what a variable is? 
  C-h v <the name> RET

Then, for what OP wants:

  touch ~/notes/notes.org
  cd ~/notes
  git init . && git commit -am "i'm taking notes!"
  emacs notes.org
  ;; type lots of notes here, you'll figure out your own best practices as you go, don't worry about it much, just take notes.

when the fundamental design goal of a tool is “if you don’t like it, change it, we won’t stop you and we’ll even show you all the knobs and dials”, and the tool has had that ethos for 45 years, there’s a lot to learn.

C-h t RET is a good place to start, and then eintr and the rest of the manuals help too.

Some people find that starter kits are good; i find that they add more confusion.