To link a trigger to a single unit you use the group mode (not sure what to call it actually) in the editor by pressing F2. Then in the same way as grouping units together you group the trigger to a single unit (you can only link one trigger to one unit). If you open up the trigger again you will notice the 'Activation' drop down box has changed and now contains 'Vehicle', 'Group Leader', Whole Group' and 'Any Group Member'. These are all pretty self-explanatory except that 'Vehicle' means the specific unit you grouped it to, regardless of whether they are in a vehicle or not.
A small trick I use to ensure that the trigger is set up properly and activated when it should be, is I use this line
This will make it so that when the trigger is activated you character says "Trigger Activated" so you know the trigger has definatly been activated.Code:player sidechat "Trigger Activated"
So is your character says "Trigger Activated" but nothing happens then you know it's the code you used that is the issue and not the trigger parameters.Code:bomb = "Bo_GBU12_LGB" createVehicle getmarkerPos "explosion"; player sidechat "Trigger Activated"
Armed Assault Editing Guide - Deluxe Edition
(most should still apply to Arma 2)
combined with this:
Arma 2 Command Reference
should help a lot with other aspects of editing.
For a grenade sized explosion, this should work:
Code:grenade = "grenade" createVehicle getmarkerPos "Markername";