Roles in Ministry Grid are two-fold. 1) They allow you to easily give certain people in your church the ability to manage and edit certain parts of Ministry Grid while 2) also allowing a level of organization of users based on the role that people play in your church.
By default, Ministry Grid gives you two main roles - Participant and Admin. You can create new roles if you'd like. Below is a screenshot of the different permissions you can set for any new role you'd like to create. Simply use the toggle switches next to each permission to turn them on or off for that particular role.
To find your current roles, or add new ones, click on your Organizations tab at the top of the screen, then select Manage Roles.
All users will automatically be assigned the "Participant" role which gives them no permissions. This is regardless of how they are invited into your church or organization.