You can either enter a game or a position. Select the preferred mode in the Play/Edit menu which is located right above the board.
In play mode colors toggle every move and Japanese Go rules apply. Use the cursor keys to navigate through the game.
In edit mode you can use the mouse buttons to add and delete stones on the Go board. The left button adds black stones, the right one adds white stones, the middle button removes stones.
In both modes: if you would like to start with an empty board again you select the Clear button, located just above the board:
You will notice that while entering a position the Search button is not yet selectable. You need to specify a search region as well before you actually can give the search command.