- Select the piece you want to move by "clicking" on it ... only pieces which can be moved can be selected - the cursor changes from an arrow pointer to a hand over these pieces.
- Click on the square you want to move the selected piece to ... again the cursor changes to a hand to indicate which squares are vaild - invalid squares show the arrow pointer.
- Click on the appropriate button below the board (the first button will record the move and then take you back to your main page, the second button will record the move and leave you at the current game, and the third button will record the move and take you to your next game). There is also a button to cancel the move slightly below these three. The buttons only appear after you have made a valid move.

You seem to have made a move already so hopefully you have worked it out :)