There you can manage most files and subfolders intended for a average user, it contains the following folders:
The bios folder has to contain the BIOSes files used by Recalbox consoles emulators, please note that some emulator do not require any BIOS to work.
Cheats Cheats downloadable via the Retroarch menu.
Extractions This is where your zipped roms will unzipp before launching the game.
Kodi Place the media you want to play with Kodi here in the corresponding sub-directories.
Lost+Found When a disk crashes we use the fsck program to repair (equivalent to scandisk); this is where he deposits the fragments of lost files.
Music Place your files here to replace the default background music in emulationstation.
Overlays Place your overlays here to customise the outline of your screen when a game is launched.
Roms Place your roms here in the sub-directories corresponding. The roms folder contains multiple subfolders, one for each supported system, each of them contains a readme.txt file describing the supported game format for each system. The games are meant to be inside those, you also have gamelist.xml files, and potential media subfolders. The gamelist.xml contains informations for each game, in a way EmulationStation can understand, and the media subfolders contains images or videos to be displayed along the games in the game select screen.
Saves Directory where your game saves are stored.
screenshots Directory where your game screenshots are stored
System Recalbox configuration and system directory.
Themes Place your themes here for the EmulationStation interface of your Recalbox.
The folowing folders are related to the games, and should be backup frequently to prevent any loss, it is also wise to back them up before updating just in case.
The music and themes folder can be used to customise your EmulationStation.
By putting musics in a ogg vorbis format inside the music folder, EmulationStation will use those musics instead of the default ones.
You can also put custom themes inside EmulationStation and enable them using the system menu.