if you want an easy grenade spell that does the exact same thing as the one that guy posted (without triggers..), then
Create a new ability based on 'pocket factory'
Create a dummy unit with a model file that looks like an explosion. (the neutral explosion in the spawned effects category works nice)
don't forget to remove shadows, add the ability 'locust' to the unit, and important: give it 1 hp, with -2 regeneration (hold shift and double click it so you can make it negative)
Create another ability based on Kaboom
Set all the damage on that kaboom to what you want your grenade damage to be.
give your dummy unit this kaboom ability.
then go to the pocket factory spell (this is your grenade spell), name it Grenade throw or w.e, then change the projectile file to a grenade being thrown or something, and make the factory unit = to your dummy unit.
the leash range and w.e doesnt really matter since the unit will just explode right away.