Microsoft Teams is a chat-based collaboration workspace within Office 365.
Get help (microsoft support docs)
The web app is a bit of a dumpster fire, but if you need it, you can find it here
In the top right of your screen, there is a "gear" icon that represents Settings. Click that and make sure that you have the appropriate mic and camera selected.
Open the Teams app. On the right hand side column, click Meetings. You should see your meeting and be able to Join it (top right)