Latex to render mathematical and scientific writing. Also check out this LaTeX introduction. Essentially on GitHub can be used on some websites like Stack Overflow or to write.
Markdown which is a markup language that is a superset of HTML.
Visual Studio Code comes with an integrated terminal. By studying the document source code file compiling it and observing the result side-by-side with the source youll learn a lot about the R Markdown and LaTeX mathematical typesetting language and youll be able to produce nice-looking documents with R input and output neatly formatted. Im a programmerjust let me use LaTeXs equation format instead. Also check out this LaTeX introduction.