In the meeting invite, select Join Microsoft Teams Meeting.

If you don’t already have the Teams mobile app, you’ll be taken to your app store to download it.
Download and open the app. If you have an Android device, open the app right from the app store page.
If you have an iOS device, tap the meeting link again to open the app. Teams will ask if it’s okay to use your mic. Be sure to allow it so others in the meeting will be able to hear you.
Next, you’ll be given two options for joining your meeting: Join as a guest or Sign in and join. Choose Join as a guest.

Type your name and tap Join meeting.
This will bring you into the meeting lobby from which you will be admitted into the session.