i've seen this in many games but i dont know how to set it up. any one know how to make this work?

basically, move the bunker to another location after the units have been loaded into it, and it will fire from it's original location.

That is the way you can stack bunkers. The other way is to disable it using Set Doodad Properties. That will leave it their, and unwalkable through.

To simply cloak it: use disable doodad state on it.

To have them fire and be walkable-on, and if you're going to do this multiple times, set up an area where you stack a bunch of buildings the size of the bunker, we'll say supply depots for now. (Say they're at "Stack Location"

Conditions:
Current player commands at least 1 Bunker (or use the Bring condition or whatever)
(Whatever other conditions)

Actions:
Center "Bunker Location" on Terran Bunker owned by (Bunker Owner)at (Wherever)
Create 4 Marine at "Bunker Location" for (Bunker Owner)
(Or whatever other combination of men you like)
Run AI Script at "Bunker Location": Enter Closest Bunker For (Bunker Owner)
Wait (Long enough for units to get in bunker)
Disable Doodad State for Terran Bunker owned by (Bunker Owner) at "Bunker Location"
Kill 1 Terran Supply Depot at "Stack Location" for (Supply Depot owner)
Move 1 Terran Bunker for (Bunker Owner) at "Bunker Location" to "Stack Location"
Preserve Trigger (for multiple uses, obviously.)

Note that with this you are limited in how many bunkers you can make by how many buildings you had pre-stacked, one of them needs to die each time so that the "build space" beneath it is clear for the bunker to be moved to.

if the space the bunkers are sent to have no chance of being obscured at all, do i need to build the depot?

Or for the lazy people. Just build a bunker in this wonderful map I created a long time ago when I experimented with Cloaked bunkers. Enemys attack to the top left to prove it works >:P

The depots are only there to clear the build space. If you only need to cloak one bunker, you just need a free area. If you want to move multiple bunkers to the same location you need to have stacked buildings somewhere.