The castle rights are active (allowed) when the check boxes are marked. You can mark a box by clicking on them. To be able to turn a castle right to on, the required pieces need to be in their appropriate position (Rook and King). A thread for check may not be present also. If these rules can not be applied, the castle right can not be set!
The player’s color that may play the next move is selected by one of the radio buttons. When you choose black, the move list will show a 1. ... notation for the first move of white. Note that any previous move list is cleared when a setup is accepted.
It is recommended to save a setup immediately after acceptation for future use. This will keep you from entering the same position again.