Wire the horn wiring from the car to the Shoe Horn, the shoe horn has a provision that you can use a simple spade connector to keep it neat and secure/safe
your horn button itself has 2 wires usually, earth and live. Live will connect to the opposite side of the contact on the reverse of the hub, should already be wiring there.... The earth should connect to the tab on the horn retaining clip
If you want I can take a couple pics of the setup on my car, pictures can make this a bit easier to understand......