To login as a student of Leibniz Universität Hannover, you need a WebSSO account.
You can get a WebSSO account by activating the service "WebSSO" in the identity management, into which you can login with your LUH-ID (cf. your "Studiendatenblatt")
Maybe you already have a WebSSO account: it's the same you're using for our cloud services such as Seafile, ShareLaTeX or ONLYOFFICE.
For information on the legal basis, data privacy and other questions concerning the LeibnizCard please refer to the LeibnizCard website.