Interesting first post and welcome to our forum.
I know it isn't always intuitive what ImgBurn can do - there are several detailed guides in the guides forum, accessible from the help menu, including 2 extremely detailed guide on the settings and the functions.
Since there is no context sensitive help file (maybe someone can write one, if they are so inclined), these guides should serve as our users' first port of call.
And there is an erase RW function built in - see the Tools - Drive - Erase Disc menu.
Regards