-l, -s - I hava no idea. (s maybe size)
1200M - The size of system partition in magebytes.
-a system - the name od partition. (preload for exanple the name is hidden)
/sdcard/system.img - yes, the modified image,
/system - the mount point.
BTW, check this thread:
http://forum.xda-developers.com/showthread.php?t=2411243
I've found this 5 minutes ago
It seems that this tool works for our S3 mini, just need to edit the param.cfg file.