various files in /var/log, what are they?

From: Flip ([remove)
Date: 10/02/03

Date: Thu, 2 Oct 2003 09:23:35 -0400

I see various files in my /var/log directory. Some are called messages,
messages.1, lastlog (which is huge). Are the *.1 files older ones? The
backups? The active ones? Is there a standard type of message that goes
into the message file?

I'm trying to identify when something "funny" is happening to my server,
like the tell tale signs of an attack, etc.