To use Microsoft Teams and Office 365 you need the “Cloud Subscription” from the IT-Shop.
You can find a detailed step-by-step instruction for the subscription => here. Follow these instruction only until page 7!
Helpful information about Teams you will find here: All about Microsoft Teams
The article “Tips and Tricks for Microsoft Teams” you will find here: Tips and Tricks for Microsoft Teams
Helpful information about Microsoft 365 (Office 365) you will find here: Microsoft 365 – IT Knowledge Base – Confluence (ethz.ch)