Hi December. Welcome to the board. Your problem is that for Portal (set & return) you don't have enough skill in Air. For a level 5 spell you need about 60 pts in the skill as well as what you have in what ever book necessary - example Wizardry. You can Train the skill up by useing Air spells every battle and eventually points will get dropped in. Check out the Tips Tread, there is a very good chart that explains this all much better.
Best of Luck