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.

Choose your institution from the drop down menu. If you have a Swiss edu-ID, choose 'Swiss edu-ID'. You will be redirected to your institution (or Swiss edu-ID Page) where you can provide your credentials.

Go to https://toolbox.switch.ch/ and click on the link "Create a Swiss edu-ID".
Fill in the form and check your inbox for the confirmation email. Click on the confirmation link and continue with the login process.

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. 

Please see the Quick Guide on how to create groups.