Selecting Transparancy Color in Gimp

I want to paint in transparancy, as well as cut out areas of an image, leaving
transparancy behind, but all I can do is work with selectable colors,
gradients, and patterns, current color settings, etc. How do I activate
transparancy so I can do this?

Thanks.



--
Rick Rosinski
http://www.rickrosinski.com
rick@rickrosinski.com