If you are referring to custom collision shapes, GS does not have that yet. You only have square or circle to choose from. You have to design your character with no extra space around it.
You could create another smaller actor (with alpha 0), constrain that one to your character and then use that smaller actor as your "hitbox" actor (so your enemy actors would collide with the smaller hitbox actor instead).
Answers
I'm guessing you mean transparent, create a new image, set it as transparent, save it as PNG, not much to it.
no I mean the image is a square and my character isnt. how can I make the image only aiming at my character and not the empty transparent space
If you are referring to custom collision shapes, GS does not have that yet. You only have square or circle to choose from. You have to design your character with no extra space around it.
You could create another smaller actor (with alpha 0), constrain that one to your character and then use that smaller actor as your "hitbox" actor (so your enemy actors would collide with the smaller hitbox actor instead).