Note that I am about to give you the simpletons version of registering a system. Expect nothing fancy below. In this post I will do my best to keep it brief. If you need to register newly build RHEL 7 system using Subscription Manger rather than the rhn_register command (which is pretty much deprecated) you will need to run the command as shown below. Including the option "--auto-attach" is pretty much the simplest method to register with RHN, as you do not need to keep track of any of your subscription names.