When creating or editing a form, you must associate the form with a program. If your program has enrollment types, you can choose to further limit the form to contacts who are enrolled in that particular type of program.
To associate your form with an enrollment type, open up the Form Builder by click on Forms in the left-hand navigation menu, selecting a form from the list, then clicking Edit.
At the top, under the section called "Current Associated Programs", click on 'Show Programs" which will reveal a drop-down menu where you may select the program(s) to associate.