Yeah, this is where Mac and PC are weirdly different.  On Mac, every regular left click is additive and you cant remove polys from your selection.  On PC you must hold down a modifier key to add to the selection... i think its control, but it could be alt.  play around with it and see.  the other key will allow you to remove polys from your selection.  I dont have a PC to test with at the moment so maybe someone can clarify that for me.

when you rotate, use the camera cube and be safe :D

selected polygons will stay selected on the item or figure you have selected, even if you temporarially move to a different one and come back or even switch tools for a bit and come back.  Try to get out of the habit of clicking in the viewport to select your figure when using this tool... use the Scene tab for that.