Please contact your host professor. They are your first and most important contact at Trier University.
Afterwards, you are welcome to get in touch with the International Office who can provide information on how to get started on campus and how to apply for access cards (e.g. for using the library and the cafeterias).
If you are staying for more than 3 months, you need to register your place of residence with the city of Trier.
Depending on your nationality, you might need to apply for a residence permit if you are staying in Germany for more than three months.