I want something like where the player hits the barrel or something with a gun and it explodes
This is possible. Put the following event on the barrel(s):
[x] [0] [0] [onProjectileHit]->[self]->[spawnExplosion]->[Vehicle Final Explosion] 1.000
The above event will make whichever brick you applied it to in the barrel explode upon getting shot. The "[x]" in it means that it's enabled, the first "[0]" is the number of the event, the second "[0]" is the event's delay, in milliseconds, and the "1.000" at the end is the scale of the explosion, "1.000" being standard size. Move the slider left or right to increase/decrease the size of the explosion.