see an overview of tex related paths and variables with tlmgr conf --only-installed
TeX related things are in a couple places: /usr/local/texlive - the installation directory /Library/TeX - binaries and documentation /Applications/TeX - where to install GUI applications (like LaTeXit) ~/texmf - user global style and bib files (changed from macOS default of ~/Library/texmf)
install packages with [sudo] tlmgr install [--dry-run] [pkg]
change location of this directory with [sudo] tlmgr conf texmf TEXMFHOME=[path] (normally it's stored under ~/Library/texmf in mac) the file that this writes to is /usr/local/texlive/2020basic/texmf.cnf
directory for global .sty, .cls, .bib, .bst files, the order for searching is /usr/local/texlive/2016/texmf /usr/local/texlive/2016/texmf-dist /usr/local/texlive/texmf-local
the first two are managed by the install, the second is local to all users on the computer
this directory is specific to a user, the path to be searched can be found at tlmgr conf | grep 'TEXMFHOME'
place .sty, .cls files in [texmf]/tex/latex place .bib, .bst files in [texmf]/bibtex/bib