If you have an MPCDF user account you can log in to this platform to manage the MPCDF services you are subscribed to or invite external guests to use them. If you have a guest account you will not be able to log in here. You can go right to the service you were invited to and collaborate with your inviter there. The services provided by the MPCDF for guest users are:

DataShare (https://datashare.mpcdf.mpg.de)
DataShare is a file-sharing platform based on the open-source collaboration suite OwnCloud. Regular users are granted a storage quota of 100 GB. As a guest user you will not have your own quota but share your inviter's DataShare storage.

GitLab (https://gitlab.mpcdf.mpg.de)
GitLab is a web-based open-source DevOps lifecycle tool that provides a Git-repository manager with wiki, issue-tracking and CI/CD pipeline features.