The Fill Tool replaces parts of the currently selected layer with a constant color.
The Fill Tool can either fill the entire image (high tolerance), or only parts of the image with similar colors (low tolerance).
In addition, the color fill will be clipped to the current selection.
If the "Contiguous" option is enabled, only parts that are connected to the starting point will be filled.
If the "Contiguous" option is disabled, similar colors will be replaced within the entire current image layer.
The current foreground color will be used as the fill color.