If you are doing something custom and not following a diagram, you just have to understand how it all works, luckily it is pretty simple. It helps to separate things out and tackle them one at a time.
First, everything besides a switch will need a ground, whether it is a wire, or self-grounded by mounting it to metal. Grounds are typically black wires. Power just needs to be delivered at the right time, either with the ignition switch or through a separate switch like the headlight. A test light is your friend for finding power, use a multimeter to figure out switches.
Cut the headlight wires and make sure they aren't touching anything that will short them out. Put the headlight switch on low and test the wires for power with the key on, some bikes need the engine running. One of the three wires will have power, the other two won't. Now switch it to high, the wire you found before will no longer have power, but another one will. That is your high beam, the one left is the ground.