Ableton's official Learn Live series walks through the Places section of Live 12's browser, the home for all your custom content. The section covers four distinct areas: Packs, User Library, Current Project, and Add Folder.
Packs is where you download and install any official Ableton packs you own. Installed packs appear at the top, available ones sit under a separate tab, and right-clicking any pack surfaces more details before you commit to downloading.
The User Library is your personal storage space for custom presets and content. It comes with a set of predefined folders that should stay intact, but you can add as many of your own folders as you need.
Current Project shows all files and folders tied to whatever session you have open. Add Folder lets you pin any external directory directly to the sidebar, which is the quickest way to get your own sample libraries accessible without moving files around.