Most reports include filters which allow you to limit the data shown according to certain parameters. These vary based on the report you are looking at but may include:
Scheduled and/or Actual (if you have Time and Attendance on your account)
Published and/or Unpublished
You can set your filters at the top of the page by clicking on the dates (reports show information up to one year) and icons.
Click on the icon to open the filter. This will show a popup allowing you to specify which items appear in the report.
Simply click Apply to enable the filter.
To disable a filter, click on its icon, click Select All, then Apply.