You have a 3 gang light switch, and each switch has 3 connections. One called common, and the other 2 marked as L1 and L2. The power goes into the common connector, and comes out of the L1 connector. So the first thing you need to do, is find the live red wire, and put that in the first common connector. Now none of the other red wires should be live(but make sure they don't), so take one and put it in the L1 connector and see which light comes on, and then mark that wire and take a note of it. Then do the same with each of the others, and put them in the L1 connectors of the other switches. Then you take the small brown wires, and connect them between the 1st switches common, and the second switches common, and then from the second to the third. And one of the switches will have had 2 wires in it so that 2 lights come on at the same time, so there'll be 2 wires in one of the L1 connectors.