Connect terminals with same name on the boards together by some piece of wires (You can use the extra legs of the other components). Solder the Back board to the Top board. Solder the Front board to the Top board. Bend the wires and put three boards on the battery holder and solder Front board and Back board to the Bottom board (Use some long flexible wires to contact terminals of the Back and Bottom boards). Connect + terminal on the Top board to the battery holders + pole.