There are either two or four log files there depending upon how web server is configured. Newer Virtual Servers are configured by default to log in the Combined Log Format. All information is logged to the following two log files. Older Virtual Servers are configured by default to log in the Common Log Format.
All information is logged to four log files.
Logged in the files above is the volume of activity at each page on your web site, the type of browser used to access each page, any errors that users may have experienced downloading pages from your site, and where users were referred from when they accessed pages at your site. The actual data logged in the web server log files is arcane, to say the least. To make any sense of it, you need a Log File Analysis Program to process and analyze it for you. Fortunately there are numerous programs that will do just that. You are free to configure and manage your Virtual Server web server log files however you like.