Groups and Topics can have their own access controls. Students can join a discussion by accessing a Topic directly, or by accessing a Group and selecting from all the Topics within the Group.
When sharing access to the Topic directly, students must meet the access control defined for the Topic. Topic Join Codes and Links are usually a random mixture of letters and numbers. Example: https://flipgrid.com/a591dc5d
When sharing access to the Group, students must meet the access control defined for the Group. Students who join the Group can then access any of the Topics within the Group, regardless of the access controls specified on the Topic level. Group Join Codes and Links are commonly customized by the educator to make it easy for learners to join. Example: https://flipgrid.com/FGrid3567
Keep in mind, when setting a Public Group, all Topics are accessible through the link, regardless of the individual Topic access controls!