how to convert garage band music into Mp3.....

first go to garage band music and click on the i to get more kinds of music of instruments.Then if you want to record your voice in your music if it appears blue instrument then you can record voice.Then when you are done go to files and save it.Then it will appear on your desktop.Then click on the itunes and drag it on the itunes.Then go to advance.Then you will see Mp3.Then your sound will be converted into Mp3.