All you have to do is to add a new integration – Trello, in this case. Once done, authenticated, and after you’ve chosen a board, you can create new cards, monitor the activity on the board, and manage and move cards – just about everything you’d need to do on Trello.
Trello is a pretty neat addition to Microsoft Teams. The integration is first of many clearly, as Teams competes with services like Slack which offer integration with several collaboration and productivity apps and services.
Incidentally, Trello competes with Office 365 Planner, a new service from Microsoft which is also integrated in Microsoft Teams. The Planner though offers limited features at the moment.