patching the kernel

[joe briggs]

My apologies for this question that is so basic to all of you, but can any of 
you please point me toward a howto or instructions for exactly how to 'patch 
a kernel'?  For example, at kernel.org, the latest stable kernel is 2.4.20, 
and is actually a patch.  I currently use 2.4.19 under Debian and routinely 
rebuild & install it no problem.  If I download a kernel 'patch', do I apply 
it to the entire directory, or the compiled kernel, etc.?  Thanks so much.

Joe