Making a usable spell usually means creating three things:
* Spell
* Magic effect (used by the spell when it is cast)
* Effect script (used by the effect when it is cast)
In the script effect you can basically do anything you like using Papyrus.
I should point out a couple of things - the CK wiki doesn't have a magic tutorial yet, but the references for the individual parts of the spell creation UI (spell creation dialog, magic effect dialog and magic effect script) are quite thorough. Between that and looking at the objects/code for an existing conjuration spell, you should be able to work it out without too much trouble.