First off, youll need Audacity. Here is the link:
http://audacity.sourceforge.net/download/ you will also need the youtube to mp3 converter. here is the link:
http://www.dvdvideosoft.com/products/dvd/free-youtube-to-mp3-converter.htm pick a song you want from
http://www.youtube.com then, download it with the youtube to mp3 converter. I wont explain how to use the converter because it is basically straight forward. okay, so once you downloaded the song, (it will already be in mp3 format) open audacity up. open the song you want, then, on the left side, next to the X, click on that button. press "split audio track", then press the X. then, press the button next to the X again, then, press mono. now, make your music. btw, you cant just save it like that, it has to be less than 40 seconds long. to cut parts off, press the scissors on the top right hand cornor. (you can only cut when the song isnt playing, and its on stop, not pause). once you are satisfied, on the top left hand corner, press "file", then "export as Ogg Vorbis", then save it at your blockland addons music folder. There you go! hope this works!!!

(BTW, FEEL FREE TO ASK QUESTIONS LOL)