How to install shower speaker
Reading the information on that page and interpolating a bit:

This is a Bluetooth speaker in a waterproof case, plus a modified shower head that it can lock into. Remove the existing showerhead and replace it with the new one (the big object). Charge the speaker (the small object), turn it on (the button), and pair it with a device that can play to a Bluetooth headset/speaker/whatever. Confirm that it plays, then mount the speaker into the showerhead by pushing it into place and rotating 30 degrees (twist-lock). When you're done using it, push the button to turn it off and save battery power.

Note that if you don't have an MP3 player or radio that speaks Bluetooth, or some other way to get the audio into Bluetooth radio packets, you can't use this speaker.