As long as their FAN has their own unique email address registered on it in Whole Game System then they can download Matchday straight away and get logged in. They'll need to generate a password if they've never logged into an FA system before - they can do so by following the link below:
If your players are under 16, your parents will all need a FAN, with their own unique email address registered on it, and they’ll need to be linked as parents to their children in your team through the parent/guardian relationship in WGS. Your Club Secretary will definitely be able to do this if you can’t, but here’s a video walkthrough on how it can be done.
Once that’s done, your parents will just need to generate their password using the same link above.