very bad tutorial:(alternate step, look on youtube)Step 1: Find a sound you like, and download it if possible. Maybe browse for no reason.Step 2: Change the extension to .wavStep 3: Realize that's all I know
Music is .OGGConvert the sound file to .OGG, then you have to script it as a sound (Not hard, it's copy and pasting like 8 lines and changing a few names). Package it (put it in a zip) and then enable it as Sound_Blah or Music_Blah