Click on the invitation link in the email you received. Log in with your SWITCHaai-credentials provided by your institution. If you don't belong to an institution of the Swiss Higher Education federation, you can create a Swiss edu-ID to join the SWITCHtoolbox group.
You are not enrolled in any group yet. You can create a new group (be aware that guests with a Swiss edu-ID can not create new groups) or join an existing group in the left column. If you received an invitation, try to click the invitation link again.