The line nearest you clips onto the roller and then through the bit ring and into your hand. The other line (on the side you can't see) just goes from the bit, through the roller and then either over the back or behind the back legs. Running it behind the back legs I find helps to get further engagement. To start with though I usually just work with it over the back and then as they warm up, move it to behind their legs. Hope this helps
I'm afraid I don't have a photo but I either use a saddle or put stirrups on the roller, then just run each line from the bit through each iron, then you can change direction without having to mess about. You could also do this without stirrups and just run the lines straight through the roller.
If you use stirrups make sure you tie them together under the horse's belly so they don't flap/bang about too much.