.diff files

[Peter Howell <pbh9545@garnet.acns.fsu.edu>]

I managed to get a base debian potato to boot on my ricoh 
g1200s.  (Everyone cheer)
Now I'm faced with my utter ignorance.  I have a couple linux boxes, but 
this is my first crack at debian.  There are some patches that let my use 
various hardware features (eg touch screen), but they come in the form of 
.diff files.  I haven't dealt with this file type before.  How do I use 
these files?

Thanks

Peter