What this step is. Getting your DMR ID requires proof that you're a licensed ham — an official FCC document with your callsign on it. This step is just grabbing that document so it's ready when you need it.
Get the “Official Copy,” not the “Reference Copy.” Anyone can print a Reference Copy from the public FCC license search, but it isn't accepted as proof. You want the Official Copy, which only you can download after logging in.
How to download it:
Save it somewhere easy to find — like your Downloads folder — because you'll upload it in Step 2.