Speakers do not have a dedicated power source of their own. They draw their power from whatever it is that they are connected to - be it a CD player or more complex stereo receiver. Any one of these pieces of equipment should be able to provide enough power for the speakers to be able to be used to their full potential. If they don't work well together on their own, an amplifier can be purchased and connected to the system to make up any power that may be needed.
Without a way to process sound information, speakers would have no function. This is why speakers are always either built into or connected to something else like a compact disc player or a stereo system. These pieces of equipment process and convert any sound information they receive (from things like the radio, CDs, DVDs) into an electrical signal. This signal is what is sent either via a wireless connection or through dedicated wires to any speakers attached to the system.
The electrical signal is then used and outputted by the speakers. What we know as "music" and "audio" is very simply the speakers playing a frequency of noise that is constantly changing. Our brains can process this information for what it is (voices, music), but it really is nothing more than noise. Settings like overall volume, base (lower frequency information) and treble (higher frequency information) can be adjusted on whatever device is sending the sound information to the speakers.