The way you've described it, one gets the distinct impression you do not have a clue as to what the history brush does and how to use it.
You need to read up on it. Read the Help files and google for tutorials.
First you need to create an image (with actual pixels in it), edit it as desired, then make a snapshot of the edited image, then target the snapshot with the history brush tool, then go back in the History panel to the step before your edits and selectively paint your edits in with the History Brush.
This one drove me nuts too and I couldn't find anything on the Net or in all the tutorials on the Adobe site. The solution I found is extremely obscure - it seems that it is critical when you take the snapshot for the history layer that you don't choose the default option in the snapshot dialog box that comes up to let you name the snapshot. In that dialog box, don't use from "Full document", instead click on the arrow button to select the option below, which is from "Merged layers" and then it worked like a charm. Good luck!
THANK YOU! I know photoshop very well (I even went back and read up on everything I already knew how to do thinking that I had forgotten a step) and this is the ONLY place that I've seen the problem solved.