Shaking Ground Spell

in many maps, i have seen custom spells that cause the ground to shake slightly and rocks to come from the ground and float up. How can i make this effect?

This was done with the use of camera triggers. They use the shake camera action. You'll have to play around with the magnitude to get the desired shaking effect. So the trigger could look somthing like this:

Event - a unit Begins casting (ability)

Condition - ability being cast equal to (ability)

Action - Camera - shake the camera with magnitude (something)
Other actions...

yea, i knew how to shake the camera and stuff but what i wanted to know is how to make the rocks and debris float up around the hero.

That effect is the earthquake effect, you probaly have to put that effect in your spell or do the trigger Create Special Effect at the place the spell was cast...I don't really know how though, I could probaly find out but im lazy

Also, for small floating rocks (outside that of the Earthquake spell), you can try a custom shrunken doodad based on the Outland floating rocks.