Well, I described what H-alpha (Ha) is in my blog, below (Moon in Ha). I have since completed processing of one of the other objects I imaged last Monday night, 23 Sep 13, and for this one I also created a "comparison" of the result (with/without Ha).
Here is M33 ... and in this, the Ha regions are clearly visible (Ha is in the red part of the visible spectrum so represented as red/pink areas), so we can see from here hydrogen emissions from 3 million light years away. Here are areas where there are exploding stars and/or star forming regions.
The "full" version and detailed imaging descriptions can be found, here: http://jeffjastro.com/dso/M33Ha_23Sep13.htm