Hi
I believe the best place to start would be the help doc. I personally prefer the 11.5 version of the help doc , i think it is more detailed.
Here are few links from where you can get to know MII's transaction better
Refer unit 4 for business logic services . It contains gud basics of transactions
http://www.scribd.com/doc/48900053/sap
The wiki link
http://wiki.scn.sap.com/wiki/display/xMII/Logic+Editor
Help doc link
https://help.sap.com/saphelp_xmii115/helpdata/en/whnjs.htm
Regards
Tufale