The IRS (and I) are highly recommending that people get IRS Secure Access setup BEFORE they need it. Right now, you need this to easily get your tax return transcript online (you might need this to file with new software) and get a missing ID Theft PIN. I suspect you will need it for more and more things as time passes.
The process is complex, and requires a lot of information. It can also take a lot of time if you don't have certain things like a cell phone in your name.
It uses your credit report as one step in verifying your identity. I'm not going to go into all the details, but here is a LINK to the information. Read it, click on the "Get Transcript Online" button, and get it setup.
The system will be operative sometime after January 9th.