1. just push the spell trigger then it shoot fireball like in oblivion
2.hold the trigger button and it'll work like flamethrower
3. equip 2 fire spells in both hand and you got large fireball (like the explosion in the trailer?)
i hope those spell usage are really in the game.
and for ice spells it could be like usual (frostball thingy) and there are variety like if you shoot the ground there would be ice spikes coming out of it or you can create small blizzard with stronger version of frost spells.
and has anyone seen bioshock infinite trailer? where the women create mini thundercloud/storm and it shoot bolts to enemies? it'd be awesome if some variety of electric spells are like that.
maybe spell growth will be controlled via perks or they will implement new mechanic.