A quick overview:
SpriteOffset defines the center point of the sprite. Divide sprite dimensions by two to find.
MuzzleOffset defines where the bullets and flashes come from in a gun.
JointOffset defines where the primary hand is placed for a gun. (trigger)
SupportOffset defines where the other hand goes on a two-handed weapon. (and, I think, a one-handed weapon without a shield-- usually the grip)
SharpStanceOffset defines how much the gun is moved when the actor uses sharpaim. (usually lifts the gun to line up with the actors eyes)
ParentOffset is usually used for AEmitters and Attachables; they define where the MO is placed relative to the parent.
Here's a more in-depth (and maybe more correct
) tutorial:
http://datarealms.com/forum/viewtopic.php?f=1&t=8694