Ok I'm going to be quite specific here, please don't take offence if you know all this.
Bluetooth is a way to connect devices, like wifi (connecting computers/phones/tablets/devices wirelessly to your home router if you have an internet connected broadband package), or a data connection via a sim card over a phone network.
So for an example, I have a TV, broadband and phone contract with Virgin Media. With this I can watch many TV channels, connect to the internet by television, phone, tablet etc. via my router wirelessly, and phone people on an ordinary telephone. My smartphone sim card comes from a different provider, GiffGaff, but that's the mobile data connection so that's not important in this context.
My computer and phone and tablet can talk to my radio/cd player/ bluetooth/digital radio device (media player, but not BluRay/DVD) via a connection protocol called Bluetooth.
Bluetooth is made for short range connections between devices in the local area. So I stream music from the internet, onto my computer, then to my music centre, which has better speakers but isn't internet connected, to play my music. I have an online internet streaming account subscription which allows me to do this. I can also connect my Kindle, a device which solely provides a way to read or buy books/texts over the internet via Wifi.
If I want to hear audiobooks, I would buy them over the internet via my computer or phone, and then stream them via Bluetooth to my media player in order to hear them on good speakers. But not via my Kindle because it's a Paperwhite and is only for text so it can't do Audiobooks. It can't stream Bluetooth to my media player.
Does that help any? Let me know where I haven't explained it properly :)