Cordless Drill: Why are sparks coming out of it

Cordless drills will usually produce some sparks at the back off the tool where the brushes are located.
The drill will make sparks when you pull the trigger and you let go off it.
Some sparks is completely normal and is generated where the brushes and the commutator connects.
If you get a lot of sparks, to the point where it shoots out of the housing, you might have a dirty commutator or worn down brushes.
Then you need to replace the brushes in the drill or clean the commutator.