BeatSaver is the master repository of custom songs made by the community. Many other tools and sites enhance the experience of downloading custom songs, but this place is where they are hosted.
If you download maps manually from BeatSaver, extract them into a folder and place the files in Beat Saber/Beat Saber_Data/CustomLevels. This is the directory that the game natively reads custom maps from.
Drag the .bplist or .json playlist file into the BMBF upload tab. A confirmation message that your playlist has been installed should appear. You can then sync the playlist into your game by pressing the Sync to Beat Saber button.
Once in game after custom levels has been loaded, a prompt from PlaylistCore to apply the playlist settings from BMBF should appear. After you accept the prompt, you should see the playlist next to the Custom Levels album's in game. Managing installed playlists can be done in-game or in the BMBF Playlists tab.
WARNING for Quest Users
Using the in game or manual playlist management methods can cause BMBF and PlaylistCore to be out of sync!
If you added or modified a playlist manually or in-game, you have to select the Reload Playlists Folder button in BMBF's Tools tab to sync changes. Otherwise, BMBF will override your settings with an outdated copy the next time you sync your playlists through BMBF.
Cross-play between Quest and PC versions of the game is now available! All players will need to be on the latest version for this to work. Additionally, modifying the game on Quest disables official multiplayer.
The BeatTogether mod is the current solution for cross-platform play between the modded game versions. Join their Discord server and check the #install-instructions channel for more information.
My game updated and now none of my mods are working
Each time the game updates it is possible (and very likely) that your existing mods will stop working and need to be updated. To make sure your install will not break when the game runs on a new update for the first time, everything in the Plugins folder is automatically moved into a new folder called Old 1.xx.x Plugins. Leave those plugins/mods in there! Please do not drag these mods back into the Plugins folder, as it is known to cause issues.
To get mods back, simply run the installer again. The BeatMods repository only includes mods that have been confirmed to work on the latest version of the game!