- TeX Live availability
- Downloading MacTeX
- About MiKTeX (in the right column there are several HOWTOs depending on your OS)
Introduction:
- LaTeX for Complete Novices (it is somehow old, i.e., don't try TeXnicCenter. Use either TeXstudion, TeXmaker, TeXworks or VSCode + TeX Workshop or emacs + auctex or another modern LaTeX editor)
- A (Not So) Short Introduction to LaTeX2ε (shorter than the first one)
Recommendation: Buy a book like The LaTeX Beginners Guide. There are many books in other languages too.
There are also al lot of other free introductions. Some of them are good, some of them are not.