What I am trying to do is very simple, combine these three cubes (http://prntscr.com/22o6q6) into one mesh to create a doorway. I’ve looked at several places but have not been able to find an answer. I want to combine these in order to easily modulate the geometry and reduce the draw calls. Is there an easy way to combine these meshes within the editor? In this video (http://www.youtube.com/watch?v=0xYdkxeEOzM) there is a doorway made from several cubes that seems to be one mesh. There is probably a very simple answer I am overlooking, but I am still a noob! If anyone could point me in the right direction that would be awesome 
You could create an empty game object and place all of the geometry onto the empty object as children.
It wouldn’t be all one mesh technically, as that would require a custom mesh to be modeled in a 3D application and export/imported into Unity, but with this option it would at least allow easy access to all three objects at once.
Create an empty GameObject called ‘doorway’. Add the three cubes as children. Position them however you like relative to each other to create your doorway. Drag the ‘doorway’ GameObject from the Hierarchy to the Project View. Delete the ‘doorway’ GameObject.
Congratulations, you have just created a prefab made up of your three cubes! You can use this pretty much like any other model asset, and it will behave like a single model rather than three separate components.
Note that if the cubes don’t share geometry and materials you’ll probably only save draw calls if you have multiple doorways in game.