Talk about how to implememt the spells(skills) in the MMO game on the server-side?

Question

I'm responsible for developing the server-side of a MMO game. Now, I begin to implement the part of fight, including player's spells. I've met many problems, for instance, how to cast a spell and to show its effects, how to caculate the damage points, etc.  If someone has the same problems or has had experience with it, welcome to talk about it, and so thank you for helping me.
Cheers!
Joseph