OK. I gave it a try after seeing your post and i think i got it.
(Note i use v1.6.4)
When you are at a photo and you want to make a selection the "Intelligent paint" works like the "Magic wand" but with a twist. If you click anywhere in the photo it selects some pixels as you would expect from magic wand BUT if left-click and hold, then as you move your mouse it continuously adds to selection.
So, you need to click-hold and drag the mouse. On top of that if you selected some area and you need to select a second area you just click on that second area and start painting the selection without loosing your previous selection. (no need to press CTRL to add to selection). Now if you need to subtract from selection you need to press and hold SHIFT (or CTRL) before doing so.
NOTE> This selection method seems to have a "slow start". What i mean is that it appears that when you first click somewhere nothing happens. If you give it a little time or if you click again and wait a while it will start painting and after that it works fine. I noticed that if you are Zoomed in it helps it start better.
Saying all that, i find this tool very old school and not that helpful. I believe, as MJR said "a simple but effective user-sizeable circular brush", that there should be a Brush for easy selection.