Greetings,
Booooooom = "HEAT125" camcreate getpos whatever
To clarify:
Booooooom - The name of the shell you are going to create. This can be used to refer to it in other scripts/ triggers. But you don't really need to do that, so just keep it there.
"HEAT125" - The type of shell you are creating. Explosions are created in OFP by 'camCreating' (the game engine's way of creating objects) an explosive shell, which will explode when it touches something. You can replace this with any type of explosive. Try "LaserGuidedBomb" for a really big explosion!
camcreate - the command to create something
getpos whatever - replace whatever with the name of a unit or object on the map. For instance, if you place a infantry soldier down on the map and call him 'Bob', you would type
getpos Bob
The 'getPos' bit is game engine code to get the position of an object.
I agree with Armsty - Head over to the Editors Depot and read some basic tutorials. For instance, snYpir's intro to script snippits.
Enjoy blowing stuff up...
-Supreme Commander PsyWarrior
-Psychic Productions Studios
More Clarification:
Set the condition of the trigger to "Radio Alpha" and click the button that says 'Repeatedly'.
Insert the code detailed above into the "On Activation" text box.
Then, when you press 0 0 1 on the keyboard while previewing the mission, a shell will go off at the position of the object you named in the code.