Two major distributions of Latex are TeX Live and MiKTeX. Overleaf appears to suggest MiKTeX for Windows, however this Stack Overflow answer states that MiKTeX is susceptible to simple viruses, and TeX Live is also strongly recommended by the Visual Studio Code LaTeX Workshop Extension (which I am using to automate compiling LaTeX documents into PDF), so I decided to go with TeX Live, which can be downloaded from here.
To make text appear underneath an operator, use \underset, as in $\underset{1 \leq j \leq n}{\max}$ (requires amsmath package, source), EG:
Use the courier package and \texttt command, for example (source):
\documentclass{article}
\usepackage{courier}
\begin{document}
This is not Courier font. \texttt{This is Courier font.}
\end{document}