[Gary Dillard]

Paraphrasing here, having just done this recently:
If you select K-12 Educator, it will take you to another section with pull down menus; one of the choices is coach / mentor, and another pull down menu that asks how you will use it has FIRST Robotics as a choice. You will get download instructions that are pretty straightforward.
Once you register for an ID on PTC.com, when you go through the software download process at some point it will ask you to login to your PTC account. At that point during installation it will ask you for a product code, which you will get in a link to more instructions. I gather that it is looking at your PTC account to make sure the code matches a license that has been issued to you. It will then begin the installation of the software that was downloaded.

PM me if you have any issues, I printed out all the instructions but I have to find them. I had to do this 3 times (my personal copy and the 2 copies we have at our build facility).