Reports can be sorted on a column simply by clicking on the column header. Web servers write log files. Every time a user visits your site, the user 'requests' information. The log file contains a list of every request made to your web server. It is full of hidden information, and it is also huge and totally boring.
Summary processes that log file and extracts the data into meaningful information.
Unfortunatly, you aren't going to be able to find out how many human people visited your site. Unsually you can make a reasonable guess, but you can never know for sure. Summary provides two numbers that are a good starting point for approximating to how many people visited. There are many different factors that conspire to make it impossible to exactly track human visitors. For example, AOL uses a proxy clustering system, which means that a single AOL visitor will produce hits on your site from a cluster of ten or more computers.