There are a number of ways to join a Teams Meetings such as from a calendar, using a link or in a channel.
Join by link
Select Join Microsoft Teams Meeting in your meeting invite to be taken to a page where you can choose to either join on the web or download the desktop app. If you already have the Teams app, the meeting will open there automatically.
Join from calendar
Select Calendar on the left side of the app to see your meetings. Find the meeting you want, and then select Join.
Join in a channel
If a meeting takes place in a channel, you’ll see an invitation to join, relevant content, and who’s in the meeting right in the channel. Just select Join.
You can login to Glow, open Teams and navigate to the Team where you know the meeting is taking place. You will see a Join button when a meeting is active.
When joining a meeting you may be held in a lobby until admitted by the meeting organiser.