3DS file formats:
.CSU = .3DS = NCSD Game Cartridge
.CIA = Installer (Citrus Installer Archive)
.CFA / .CFX = Content File Archive / Content File Executable Partition (NCCH)
if you unpack a NCSD or CIA, you get multiple CFA and 1 CFX, these are the game files
if you unpack a CFA/CFX you get romfs/exefs/manual/...
Switch file formats:
.XCI = PFS0 Game Cartridge
.NSP = PFS0 Installer (Nintendo Submission Package)
.NCA = Nintendo Content Archive (NCA2 / NCA3)
if you unpack a XCI or NSP you get multiple NCA, these are the game files
if you unpack a NCA you get romfs(istorage)/exefs/manual/...