When you create a form, you have many different opportunities to share that form with different groups of people (Admin, Teacher, Parent, Student), as well as specific Schools. In addition to sharing options, there are also publishing options.
The defaults in all these areas are to share with nobody and in no school. The publish option is also defaulted to false. By default, nobody can see the form but you (and only for modifying the form, not entering responses to it).
When creating a form, here are the sharing and publishing options:
The Publish checkbox can be thought of as a master switch, which you can use to enable or disable all sharing, regardless of the other settings. Portal share permissions can be used to set the level of access at each portal: admin, teacher, parent and student. Just click on the icon next to the portal name to cycle through the options:
Then there is Schools share permission, which allows you to choose which schools the form is shared with. By default, no school is chosen for sharing. You can choose as many schools as you want.
Options for teachers are slightly different; instead of schools, teachers can share forms with specific classes.