How To Drop All Tools.. ?

[Ofnuts]

The tools only apply to/work in the "selection". So if you create a selection with the rectangle tool, bucket-fill it and then try to use the brush, the brush will only work in the rectangle you selected. And if you didn't change the colors in between, it will paint over an identical color so you won't see anything. So, to use the brush elsewhere, remove the selection with Select>None or CtrlShiftA.