The wizardry command allows you to do initiate a mage, cast a spell and summon a spirit. Spells are cast and spirits are summoned in a given sector, and you must have a mage in that sector to do so.
Hit the [i] command to initiate a mage. Mages move twice as fast as normal armies, so they can reach a battlefield quickly to do their work.
If you have a mage already selected (see the [a]rmy menu), then you can use use [c] to [c]ast a spell or [s] to [s]ummon a spirit. The spell is cast on an object (army, or sector, or whatever, according to which spell it is) in the same sector as the mage, and the spirit is created in the same sector as the mage. Spirits must be summoned in your own land.
Most spells will hang around until their duration is over, or until you delete them, or until the army to which they apply does not exist any more. You can see which spells you have hanging with the [h] command, and that gives you the option of deleting hanging spells too. Spirits last until they are killed, and behave just like armies.