Open your web browser of preference (Google Chrome, Microsoft Edge, Mozilla Firefox etc.)
Go to https://teams.microsoft.com, you will land on the following page.
If you see your account, select it. If not, then go ahead and enter your username/email.
Enter your password and click on "Sign in".
After you are signed-in, you will land on the following page. Click on “Use the web app instead”.
Microsoft Teams will then open in your browser's tab.
Please note the functionality of Microsoft Teams on the browser is limited, it is recommended to use the desktop app of Microsoft Teams for more functionality.