There are options that you can select in the Form Builder that limits the users who can view the forms. This can be controlled by the form type, options include App and Portal (most popular) or Portal Only. Portal Only means that only Portal User types or Administration User types can access the forms.
Access to different forms can also be controlled by User Group access. In the Form Details tab when editing a Form Template, you can determine which User group/s can 'start and view' a particular form template, as well as which User group/s can 'edit submitted form template'.
To edit this for your form(s) in the Web Portal, go to Forms > Existing Templates > Edit arrow for the desired template > Form Details page. You can then select what groups have access to the form functions.