Forms usually only modify reports indirectly. For example, you may have a form that controls whether or not certain features get executed. In this case, the final report isn't modified directly, but indirectly because reports always show what gets executed anyway.
You can however use the FORM/FILENAME command to pass parameters back and forth between the Edit window and a form's objects, and use Comments to cause those parameters to appear in a final report. See the "Creating Forms" tutorial and the "Inserting a FORM Command" topic for examples of this type of forms use.
Additionally, after getting the values from a form into the Edit window, you can also use the REPORT/TEMPLATE command to pass parameters from the Edit window into a report template in the same way that you use the FORM/FILENAME command.
Select Insert | Report Command | Template Report to insert a REPORT/TEMPLATE command, then assign parameter values to modify object properties in the report template. See the "Creating Forms" tutorial on how to do this, using the FORM/FILENAME command as a guide, but instead of selecting a .FORM filename, select a Report Template (.rtp filename). Also, see the "Embedding HyperView Reports or Report Templates in a Measurement Routine" topic.