As you can see, I'm really a newbie in this game..
1. Can I set An autospell to my wizard and my priest, so I just have to click on some key? It's very difficult to go over the menus and choose my spell...
2. I don't know why, but my priest can't use his heal spell. I tried to use it, but it won't work! I clicked the heal word (in the spells book), and I clicked one of my characters, and it didn't work.

Hate to say this since I hate the kind of answers when I ask a question. Howver you need to re-read the manual.
1. Any as for your question no I do not believe you can hot key spells
2. you must hold control before casting a spell on one of your characters. This keeps you from accidently attacking yourself. If you like in the game options menu you can remove this fail safe