Audacity.
Simple program, 1-select, 2-zoom, 3-finely select, 4-cut off unneeded part, 5-zoom out 6-repeat 1 to 5 for the other half of the loop, 7-and play it to test if it goes fine. 8-After that, File -> Export entire project as .OGG. 9-And last but not least - save it wherever, 10-as long as you upload it somewhere or put it in a zip and upload it. (if you want people to just extract to Blockland directory, if you know how to do so.)
10 easy steps to have winning music. Oh, and be sure to keep each music file under 500kb, or users will have a hard time to download.
Follow my instructions and you'll be making fine music
like me.