You could not make spells in WC3. You could only alter existing spells to use values you want.
In SC2 you make a spell in 3 stages.
1. Creating an effect chain, this is basically what the spell does like 100 damage or chain fires yamato gun for 10 seconds etc.
2. Create an ability and hook it to the effect chain, this is the interface between unit and effect where cooldown, charges and costs all come into play.
3. Hook the ability to a button on a unit, this is the interface between unit and user using the ability.
Not all ability types are this conventional spell cast sort. You get passive ones which add a behaviour permantly. You get training (barraks) and building (all races) and morphing (larva into drone etc) and ammo (carrier / broodlord) and cargo (bunker / medivac). You get revive and item related abilities. There are a large range but for spells mostly you will be using one of the active ones (usually with target as well).