Monitoring is only half the job. From the User sessions tab you can act on a session straight away, without opening a remote desktop connection to the server. Select a session, then use the Users menu or right-click the row.
Disconnecting ends the connection but leaves the session running on the server. The user's programs keep going, and they can reconnect later and pick up where they left off.

Logging off ends the session for good and closes the user's programs. Use it to free resources when someone is finished, but warn the user first if they may have unsaved work.

Before you disconnect or log someone off, it is courteous to tell them. You can send a pop-up message to one user or to everyone on a server.

The message appears on the user's screen right away.
That is the core loop: add servers, watch sessions, and act when you need to. From here: