There are hundreds of standard reports in Dynamics GP that are ready to go. They easily provide the basic information you need to help manage you business. They have been part of the system for years and are generally well designed to allow you to easily get to the information you want.
If you want to modify the reports, the system includes a report writer that will allow you to change the standard reports to more closely meet your needs.
This video introduces you to how to run the hundreds of standard reports that are available in Dynamics GP: http://youtu.be/F5RZ2CACBeo