Photoshop Elements 8, layers

[RonH]

Please ignore ... I have recharged my one brain cell and realised that I had not also opened a new blank file. It worked!

Help! I am very new to 'layers', have read quite a lot but cannot solve the following ... even though I have read Scott Kelby's method.
I have a black/white jpg for which I want to do the following:
Delete the background so that it is transparent ... this I can do with the Magic Eraser.
Use the black foreground (which is left ) to create a brush under Define Brushes and then use this brush to 'stamp' on to some pics.
When I select the 'B Brush' I then go to Edit and select 'Define Brush. However this feature is greyed out and is not available. Obviously I am missing some part of a process ... or it could be that my one brain cell is overloaded!