This is a simple guide on the extruder mount.
If you fill filament in and it don't enter the second or the exctuder hole, your filament is not strait.
This prevent filament friction on the extruder hole causing material to peal off.
Optionaly, it hold a filament filter: http://www.thingiverse.com/thing:497764
(ps. excuse my bad English, it's not my native language)