using diff command

[Curtis Vaughan <curtis@npc-usa.com>]

I must be really stupid, so forgive me, but I can't figure out for the 
life of me how to use the diff command. I've read the man pages and 
looked at some stuff on the internet, but I can't get it to do what I 
want it to do.  But then maybe it doesn't do what I want it to do.

Basically, the issue is this, I have 2 files: File1 File2

Both are text files. File1 was File2 a day ago. Since then File2 has had 
additional information tagged on to it (it's a log file). All I want to 
see is what information has been added since yesterday.  So, I would 
think that "diff File2 File1" should provide me with that information. 
But all I ever get is a message that the files differ.  I have tried 
with various arguments, but no luck.

What am I doing wrong?

Curtis