If you don't have a Roxio Creator (or somewhat like that) which converts your file so you can hear it on your MP3 or so, then I suggest for you to use the website: flvto(dot)com , of course you have to replace the dot to the symbol " . " for you to be taken to that website to which you just have to put the YouTube URL (which can be seen in the lower right section just below the video of the song you like in YouTube, which from the mark written in "Share" that you copied) in the blank space of that flvto and hit convert to MP3. After that, when it is already 100% ready, download it to your computer (or at least for the meantime) *note: be sure to know where you save it, for me, I save it in downloads*. After downloading it to your computer, copy (I use "cut" instead of copy) and paste it to your MP3. Remember, your MP3 is located in the "Computer" after you hook your MP3 in the computer!
And that's it, any question, just ask!