You were invited to join a family on KinBounty. This link opens in the KinBounty app - install it on this phone, then open the link again from the message it came in. Before you choose a password, the app shows whose family it is and who sent the link.
A family bounty board: tasks, rewards and points, for one household.
KinBounty is not in an app store yet. If a parent sent you this link, ask them for the app.