What are the steps for getting an MPO?
Probably the best place to start is with a victim advocate on the installation, the FAP, or at the local domestic violence program, if there is one that is familiar with your installation's practices.
Once an MPO is issued, it should be written and you should receive a copy of the MPO from the commander.* Be sure to ask for a written copy if you don't receive one. Most commanders use the recommended form, which can be found here.
The military police, the JAG office, the Provost Marshal's Office, or FAP are also resources you can contact for guidance. See also I am being abused. How do I get help in the military system? for other possible resources.
* See Department of Defense Instruction, Number 6400.06, Incorporating Change 1, September 20, 2011, section 188.8.131.52