Users who belong to multiple roles can see multiple Portal/Landing pages when they login to the site. For example, a teacher who is also a parent would have permission to see both the "Faculty and Staff" and "Parents" role landing pages - but which page would such a user see by default when they login?
The answer is determined by each role's "Sequence Number."
Open up the landing page in question, and click "advanced controls" at the upper right.
Find the "Sequence" control. This is what determines the 'default' role for multi-role users. The lowest sequence number will prevail; if you want "Faculty and Staff" to take precedence over "Parent" for users in both roles, make sure that "Faculty and Staff" has the lower sequence number.
Best practice: To save yourself a headache later, use two-digit sequence numbers for ALL of your portal pages, and number them by tens (10, 20, 30, etc.). This way you can re-order the pages anytime you want by only editing a single landing page's sequence number - turning a 30 into a 21, for example - without having to re-save each page individually.