shell125 = "shell125" CamCreate getpos logic1
You need to place a game logic at the place where you want the explosion. ANd then name the game logic "logic1"
Or if you want a really big explosion, replace "shell125" with "laserguidedbomb"
EDIT
Or, if you want a cool looking explosioon but with no dammage caused to near by objects, replace "shell125" with "explosion"