.mdl

I've been searching the internet and the forums/tutorials and I can't
seem to find anything about this, maybe its general knowledge, but i
was wondering if anyone could tell me what program is used to edit
Models in Opposing Force? or if its not a program how i would
edit models? thanks.

.mdl files are typically edited with a 3d modelling tool. For HL, most
people tend to use
Milkshape 3d
(cheap, easy, geared towards games) or
3dsmax (very costly, not too
easy, very powerful).

Before you decide which to get, look out for tutorials on modelling or
half life. I can get you started with this:
http://www.swissquake.ch/chumbalum-soft/ms3d/tutorials.html

thanks a lot

i appreciate it