First, look at the menu bar on the bottom of the screen and click on "Athletes". Then click on the little + button in the bottom right corner. Choose "New" (please note that choosing "Existing" will create a request for someone to share an already existing athlete with you). Clicking "New" will take you to the Create Athlete page where you can enter all of their info and save.
Your 6-8 ID number is the one associated with your athlete profile.