its very simple, that file is only for the track editor, but its very important too, if u wanna moddiffie it i suggest u to make a backup before, now i explain u a bit over this file:
alley.cfl 2 1 0 $ID trkdata/editor/fields.cat alley.cfl.TrackPiece <-- this format is for default pieces, its not very interesting...

# List for Crashday track editor tile categories
18 # Number of categories
these lines appear in the begining of the file, this says to the track editor the number of categories ( elevated, dirt road, tunnels, tunnels 2...) if u add a new tile or a categorie with new tiles u must change this number or u wont add the new tile with succes. 4 example if u have 12 and add a new tile u put 13

i have 18 because i have added various new categories, u should have over 13 i think, lets continue:
Next: # CFL file / PositionX / PositionY / Rotation in display
jose test # Name
1 # Objects per category
jm_dirt4sjumper.cfl 5 1 0 test
this is the format of a custom tile:
-"jose test" is the name of categorie, like tunnels and those things
-"jm_dirt4sjumper.cfl" is the name of the cfl file of the new tile, the cfl must be in trkdata/tiles
-"5 1 0" this refers to the position of the piece
- "test" this will be the name of the trackpiece in the track editor
its all 4 now, i hope have helped u
