The Webalizer uses the gd graphics library written by Tom Boutell for producing it's inline graphics. If you don't have this library or have it installed correctly, you will get this error. If they are located somewhere else, you can either create a symbolic link to them, or edit the Makefile and specify the correct location. There is an on-line quick help that explains most of the major terms and headings used in the reports. Basically, HITS is the total number of HTTP requests that the server received during the reporting period.
Any request made to the server is considered a hit.
Total Files' and '200 - OK' totals should be the same. If you add up the totals in the 'Hits by Response Code' section, it should be the same as the 'Total Hits' figure. There is also an Webalizer Quick Help document on-line that explains the most common terms used in the reports. With the release of version 1.2x, The Webalizer now supports incremental processing. This allows you to rotate your logs as often as needed without the loss of statistical detail between runs.