https://blogs.technet.com/b/pfesweplat/archive/2012/10/15/step-by-step-walkthrough-installing-an-operations-manager-2012-gateway.aspx

This is a post I wrote in 2012, and since it has been helpful for a lot of people this is the link:

https://blogs.technet.com/b/pfesweplat/archive/2012/10/15/step-by-step-walkthrough-installing-an-operations-manager-2012-gateway.aspx