There are three things for you to do now you've accepted your account invitation.
1. Do some modules!
You'll have access to one or more of the courses: Fleet Driver Plan or another course, the sections under Learner Licence (Car, Heavy Vehicle or Motorbike) or Tourist. Some options might have been hidden by the person that invited you. Car, Heavy Vehicle and Motorbike sections are for learner drivers.
Once you've completed some modules they will appear in the Your skills section.