Download and Read IRS Publication 3112
IRS Publication 3112, IRS e-file Application and Participation provides a clear, step-by-step explanation of the Authorized e-file Provider application process. It's a quick read. You may want to download and save it so it's easy to refer to if you have questions along the way.
Publication 3112: IRS e-file Application and Participation (.pdf) for more about the process, required software, etc.