You purchase all of the components.
Next take all of them apart and use the parts that you need.
After everything is taken apart you have to solder everything together. I like to start with making the two speakers one and after I've done that I solder the 1600 battery to the main chip so the speakers have a lot of power to use.
Next start making a frame so that way you can put everything inside. Make sure to cover up all of the openings so no water can get in.
After all of that I filed a old GoPro mount I had and attached to the side of my new frame for the speaker.
After the entire speaker was assembled a mounted the iPhone on top of it and connected all of it to the speaker. Making it one piece of hardware.