There are many levels of filters available to you when viewing reports:
All these filters are combined when used together; i.e. an item is included if it is selected by the Filters AND by the Date/Time Filters AND by the Zoom Filters. For instance, if the Filters show events during 1am-2am, and the Zoom Filters show events on January 1, then the table will show event from January 1, during 1am-2am.
The filters that are applied to the report determine what statistics you see. The Filters let you "zoom in" on one part of your data (in a similar way to selecting a new view from The Report Menu). You can use the Filters to get information about a particular day, or a particular directory, or a particular domain, or more.
If there are no filters in place, that means you are looking at your complete data; all available data is represented by the graphs and tables shown. If the The Report Bar shows that there are filters active, then you are not seeing your entire data; you are seeing only a portion of it. What portion you're looking at depends on the Filters. If, for example, the only filter is a /dir1/ filter on the page field, then the data displayed shows only those hits which were on /dir1/ or pages contained in /dir1/ (or in other directories contained in /dir1/, or pages in them, etc.). For instance, if you have 1000 hits on your site, and 500 of them were inside /dir1/, then if there are no filters active, you will see 1000 hits in the tables and graphs, or all the hits on your site. But if there is a filter /dir1/ on the page field, you will see 500 hits in the tables and graphs, or only those hits in /dir1/.
The Filters are an extremely powerful way of getting detailed information about your site. If you want to know what day you got the most hits on /dir1/, you can do that by adding /dir1/ as a filter, and then changing to the "Years/months/days" view (see The Report Menu). With /dir1/ as a filter, you will see only those hits on /dir1/ (500 of them, in the example above), and you will see how those 500 hits break down by date and time. You can add an additional filter to the date/time field if you want to examine just the hits on /dir1/ on a particular day. This gives you almost infinite flexibility in how you want to examine your data.