To add new terms:
Log in as user with the site admin role.
Open the admin wrench and navigate to Structure > Taxonomy.
Click "List terms" next to "Question category."
To add a term click "Add term" in the tab at the top of the page.
Type the term name into the "Name" field and click "Save."
To create a hierarchy of terms:
Log in as user with the site admin role.
Open the admin wrench and navigate to Structure > Taxonomy.
Click "List terms" next to "Question category."
Drag and drop to up and down to re-order.
Drag left and right to create hierarchies.