To preview forms and schedules, from the menu bar, click on View > Detail/Forms View and choose either option.

If the input screen is for a specific form or schedule, the form number will be displayed in brackets () next to the description of the input screen on the General tab under Table of Contents.  If certain section or line item on the input screen is associated with a particular form or schedule, you will see that on the input screen as well either as a description or header.  There are, however, also some input fields that do not have any such reference but you will learn in time what those are related to.

If you are looking for the input screen for a particular form or schedule, you can also drill down from the field on the form/schedule with a right-click and select "Jump to input".  See my other response for how to preview forms.