How does a docking station work for a mp3 or 4 player?

I was thinking about a docking station for the mp player, how does it work. Does the docking station require batteries, and if the mp player as inbuilt batteries would this be affected? The answer with the most details will win the question.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).