You write in the air. What you write happens immediately. The scale of possibilities is something like this.

Level 3- Move and object.

Level 4- Blast an element.

Level 5- Summon a creature 3 challenge or less.

Level 6- Summon any monster.

Level 7-  Control Something

Level 8- Create something within a 100x100x100 ft area.

Level 9- Wish (same effect as the spell of the same name).