To make an explosion at a certain place: First, let's make us a marker where we want the blast. I'll call my mine "boommarker". Assuming you're doing this in a cutscene, use a script that executes at the beginning of the mission, waits until you want the blast, then detonates. Copy this into a text file, name it (Anything You Want).sqs and put it in the mission file. Voila! You got your self a huge bang ;D wherever the marker is.
;Script Begins Here
_boom = getmarkerpos "boommarker"
_bx = _boom select 0
_by = _boom select 1
_bz = _boom select 2
_power = "heat73"
_tempobj = _power camcreate [_bx,_by,_bz]
~0.01
_tempobj = objnull
exit
;Script Ends Here.
Switch "heat73" to the name of any explosive to get a good blast power. Here's the names:
heat125, shell125, heat120, shell120, heat105, shell105, heat73, shell73, mortar, grenadelauncher, and handgrenade.