When you receive the link just click on it and you will be taken directly to the Family Tree.
This is a view only screen but to enable editing of the whole tree you need to sign in.
If you have a Family Echo account then just sign in as usual otherwise create an account.
You will be taken directly to the family tree with full permissions.
You do not need to use the link again. The next time you want to view/edit the family tree then sign in to your account.