The pod is a zerg unit (I forgot the name) and automatically does the falling from the sky/breaking open animation when it is created. Once the animation is done, just create new units at the impact location. I don't believe you can 'load' units onto the pod like you would a medivac, but haven't tried.
Rollback Post to RevisionRollBack
Current Project: Diary of a Drone - A Bound style map with a touch of Frogger and Lemmings.
The unit is called a drop pod and it's created by a trigger called "create drop pod" (or some variation on that name, I can't quite remember off the top of my head :P). The trigger is only available if you have the campaign dependencies enabled. In the options list for the trigger you can select either a Zerg or Terran drop pod model. Hope that helps :)
What Chromium said. 'Dependencies' are basically 'versions' of the game - normally you're stuck in the multiplayer dependency, which means you only have the normal units and upgrades at your disposal. You need to go File > Dependency and set it to campaign dependency so you get all the neat stuff from singleplayer. The drop pods are in that dependency.
Additionally, to answer your explosion question; I'm pretty sure the explosion is trigger-based, though you could probably make it data-based if you were so inclined. You can open up the map yourself (just go to the 'campaign' tab when you click on 'open map) and have a look, if needed.