Dwarf needs to collect magic goos from this thing called magigoo. The way to collect them is by drawing a circle on the ground using his magic chalk. Goos inside the circle will be placed in jars. But goos in jars can be reduced if Dwarf miscaptured badgoos, so watch out :).
Use Mouse to navigate Dwarf and draw the line (by pressing the left mouse button). You need to at least capture 2 goos of the same color to collect them. The more, the better. No other keys except for ESC to pause and unpause.