It has a very specific shape so you will notice with the square shape of your cursor you are in eraser-mode. The small one is designed to use when drawing thin lines or inking. The large one is for removing large portions of a layer (eg. This page illustrates and describes the included default brush presets in Krita 4. Show a sample of what the brush engines can do.
Propose tools for the various ways Krita is used: Comic inking and coloring, Digital Painting, Mate Painting, Pixel Art, 3D texturing. Help the beginner and the advanced user with brushes that are ready-to-use. This collection was designed with many considerations: Krita comes with a large collection of brush presets.