The easiest way to register with the MHSAA is on-line at:
http://www.mhsaa.net/Officials/Regis...n/RegBegin.htm
You can also send an e-mail to request the necessary materials via mail. There's a link in the first section of this page to do so.
http://www.mhsaa.com/resources/official.htm
After you fill out your registration materials and pay your fees you will be sent an open book rules test and another test regarding MHSAA policies and procedures ( If I remember, one of the questions was: What is the address of the MHSAA?) This was several years ago and I'm not sure if the testing portion has changed. They will then send you an id card and your patches.
I would also recommend finding the nearest association (they are also listed on that above page) and making contact with the person listed. They will be helpful in either putting you in touch with an assignor or getting you in the mix to get games. Association membership is also beneficial since you have to be a member in good standing of an association to have any post-season assignments.