Get a wand from either the /Okit command or a server op.
Start hitting the books and learning some spells. Cast them over and over again to gain experience!
Create a Spell Journal! Sign a book with the title "Spell Journal", and when you read it two times in a row, it will display your known spells and their levels.
Study transfiguration to transform the world around you! Start by reading "A Beginner's Guide to Transfiguration".