Begin by entering a puzzle.
Use the "Input" button to enter given (black) digits one at a time.
Use the "Rapid Input" button by selecting multiple cells, hitting the button, and then entering those given digits in sequence (left-to-right then top-to-bottom); this mode is useful for rapid entry with a keypad.

Cells can be pencil-marked with normal (full-sized), corner, center, and color marks.

Different highlighting modes are available, which will highlight like-numbered cells based on your current selection.