Krita's fill tool reference. New in version 5.1: Spread. Set how far the fully opaque portion of the region should extend. 0% will make opaque only the pixels that are exactly equal to the selected pixel. 100% will make opaque all the pixels in the region up to its boundary.
The hotkey can be edited in Settings ‣ Configure Krita… ‣ Shortcuts. The sticky-keys can be edited in Settings ‣ Configure Krita… ‣ Canvas Input Settings. Tool Options¶ Smoothing¶ Smoothing, also known as stabilising in some programs, allows the program to correct the stroke.
When you first invoke the tool, handles will appear at the corners and sides, which you can use to resize your selection or layer. You can perform rotations by moving the mouse above or to the left of the handles and dragging it. You can also click anywhere inside the selection or layer and move it by dragging the mouse.