link not working
but usually its just:
patch <original file> <patchfile>
all it does is run diff on it and only changes the original file based on whats different tween it and the patch
to do a directory I think you need to use the -p"#" option if you want to exclude parts of the directory tree involved
its been awhile since Ive used it, might try googling for kernel pacthing, thats the last thing I used it for and as I recall the command was listed too, that way you get an example