You can use the keyboard to enter numbers, the arrow keys to move around, and Tab/Shift+Tab to switch modes. Backspace and Delete can clear all values in a cell for the current mode.

Use the Center mode for entering numbers that the cell is restricted to. Use the Corner mode for noting which cells a given number is restricted to. The Color mode can be used for additional annotations.

You can export the full current state of the board using the Share current state button. This will export all annotations but not any undo history.

You can export the current state of the board as a new problem using the Export as problem button. This will not export any annotations.

The Reset button will reset things back to the original problem state.

The Select confirmed toggle will allow you to select cells which have "confirmed" (i.e. "main") answers.