To place a piece on the playing board, first highlight the 5 spaces on the board where you want the piece to go.  (If you’re just starting out, you can see what each piece looks like in the pieces palette — check Options/Show pieces palette while playing.)  Keep in mind that any piece can be rotated and/or flipped to fit on the board.

To actually place a piece after you’ve highlighted the appropriate squares on the board, hit <RETURN>, <ENTER>, or select Options/Place piece.  To remove the last piece you placed, select Edit/Undo.  You can also remove any piece you’ve already played by double-clicking on it, or clicking on it once and hitting <DELETE> or selecting Options/Remove piece.

You may use each piece only once.