Before diving into the different file formats this page will give a quick overview about files and which formats there are.
The game folder often only exposes a couple of files (usually bink video files), all the other files are located in the Bigfile.
|.drm||Data Ram||See Data Ram|
|.mul||MultiplexStream||Music, sound and cinematic container format|
|.raw||RAW Texture||Raw texture/image|
|.mus||Music Script||Controls music flow|
|.sam||Music Sample||Music samples|
|.ids||IDMap||Key-value file to lookup names from ids|
|.sch||SchemaFile||Strings entry file (often subtitles)|
|.dep||Unknown||Some build process file|