How to listen to music in my car other than through a CD?

I have a VW Golf, and inside it doesn't have a USB port connected to the stereo. The only thing it has that I can plug stuff into is an adapter thing (I think a lighter would usually be there, but it just has a lid you pop open and plug stuff into) that says "V12" (I have no clue what that means)-- which I plug my GPS and phone charger into. I'm not a car person, I don't understand anything relating to care other than how to go to point A to B.
Can I put anything into the plug that says "V12" to play music through the car stereo? Is there a Bluetooth I can plug into it or something that I can connect my iPhone 5 to? My phone charger has a USB connector in it, can I plug a USB into it to play music?

Like I said before, I have no idea about anything car related, the only way I found out about the adapter thing to put my GPS and charger to is by sheer luck, and the fact that the thing I bought fit in it.

Try reading the car's manual about hooking up a Bluetooth connection (this involves syncing the car to your ipod wirelessly).

Really, it should be 12V not V12 as it's telling you it's a 12 volt receptacle. Why do you think you could plug something in there to have sound come out of your speakers? The fact that the "thing" fit into it is no different than you buying a TV or vacuum cleaner and plugging it into the wall in your house.

If you don't have a bluetooth radio or an axillary (aux) input somewhere on the radio, then no, you can't just magically play music without a CD or new radio. Depending on the year of the car it may or may not be likely.

YES, you can!
Besides your CD player, I'll assume that you have an AM/FM radio too (almost all cars do.)
Do a search on eBay (or your favorite site) for "fm mp3 transmitter". For as little as a dollar or two you can plug these things into that 12V 'cigarette lighter outlet' and you can play your own assortment of MP3 songs from your personal collection (or from a friends collection) by plugging in a USB flash drive (thumb drive), an SD storage card, of even hook it to your smartphone and play the songs from your phone - through this device, over your FM radio!
I have one in each of my family's cars. We all love it! Each of us has our own collection of music on a chip (SD card) and it's like having 'pandora satellite radio' service, at no charge.