/var/log/httpd/access_log and /var/log/httpd/error_log
A simple [b]tail /var/log/httpd/access_log[/url] will show you the last few lines from the log file.
Once you're into looking at your logs, you might want to switch to the "combined" format, which puts your referer and user agent data all on one line. You can do this by editing the Apache config file at /etc/httpd/httpd.conf.
You might look into installing
Webalizer if you want to see nifty stats.