How do you do this?
First, make music using Little Sound DJ. More info at the LSDJ homepage.
To extract your .LSDSNG file from your Little Sound DJ .SAV file, download and run the LSD-Manager, load your .SAV file, and save your desired .LSDSNG file to your hard drive.
If you use custom kits, extract them using the LSD-Patcher and post them along with your songs.