Verify that you are on the correct spellbook. Air strike should be the highlighted spell in the book on the left.
If you see something like the book on the right you're not on the standard spellbook. If you're F2P you shouldn't have this problem.
Selecting a spell from your book will not cast it, it will only load it up as your autocast spell. To move the wisps in Rune Mysteries, you need to select any wind spell as your autocast, have the mindspike equipped, and then click on the spellwisp to attack it.