Where's My Stuff?
The GUI applications used to interact with TeX are installed in /Applications/TeX. These applications are BibDesk, LaTeXiT, TeX Live Utility, and TeXShop. This location contains a file named "READ ME FIRST" which explains how to get started using TeX and LaTeX with TeXShop.
MacTeX installs TeX Live in /usr/local/texlive, a standard Unix location for additions to the system. In particular, TeX Live is placed in /usr/local/texlive/2024 and BasicTeX is in /usr/local/texlive/2024basic. Obviously the year, here "2024", will change with each new release.
These locations are not visible in the Finder by default. A symbolic link to the currently active distribution is in /Library/TeX/Root. Users can use this location to examine files in their active distribution. There are a lot of files! Users can also access the Finder's "Go" menu and select the item "Go To Folder". Fill in the location "/usr/local/texlive/2024".
Personal files should be stored in ~/Library/texmf. (Recall that ~/Library is the library folder in your home directory, while /Library is a system folder analogous to /Applications.) You will have to create the subfolder "texmf." This is a spot for style and class files from publishers and other files not in TeX Live. When TeX needs to open a file, it searches ~/Library/texmf first, so if you place a standard TeX Live file in ~/Library/texmf, that copy will be used even if TeX Live later provides a bug fix for its file. So putting standard files in ~/Library/texmf is usually a bad idea.
The folder structure inside ~/Library/texmf should mimic that of the texmf trees in your TeX distribution. This is easier than it appears. TeX will locate any file in ~/Library/texmf/tex or in a subfolder of this folder; LaTeX will locate any file in ~/Library/texmf/tex/latex or a subfolder of this folder. Bibtex will locate any .bib file in ~/Library/texmf/bibtex/bib or in a subfolder of this folder, and any .bst file in ~/Library/texmf/bibtex/bst or in a subfolder of this folder. Etc.
Ghostscript is installed in /usr/local/bin and /usr/local/share/ghostscript. We compile two versions of Ghostscript, one named gs-X11 with X11 support and one named gs-noX11 without this support. At install time, MacTeX checks to see if XQuartz is installed on your Macintosh. If so, it creates a symbolic link gs --> gs-X11 in /usr/local/bin. Otherwise it creates a symbolic link gs --> gs-noX11.