Good to see more players eager to give Fantasy a try, I will also be there next Tuesday and will be happy to teach new players the basics. I understand that most people that first learn fantasy already know how to play 40k, so here are two very broad bits of info differentiating the game systems ..
1) Unlike 40k, where 50% of the player base are Space Marines and 50% is "everything else", Fantasy has no dominate race.. everytime you play against someone you literally have no idea what army your facing. Almost all the armies are great fun and play very differently from each other.
2) Fantasy is divided in 4 phases instead of 3 like 40k.
-Movement
-Magic
-Shooting
-Assault
Unlike 40k psychic powers, magic plays a MUCH LARGER role (thus getting its own phase)
So I will leave that for the new guys to think about (and hopefully after reading this you didn't go mad and start having laughing/screaming fits lol).. Welcome to Warhammer Fantasy; come back with your shield.. or on it!!