Joining via Smart Phone
You’ll need a Google account to use the smartphone app. The app won’t allow you to join a meeting without signing in. If you need to create a google account, go to www.google.com, click "sign in" at the top right, click "create account" and follow the instructions. Once signed in, you can tap “Enter a Meeting Code”. That’s the code that’s at the end of the URL - above example is: mfm-mfwt-dtw (you don’t need to enter the dashes).
Joining via Telephone (PSTN)
Simply dial the phone number in the meeting invite and when prompted to do so, enter the PIN followed by the “#” on your phone keypad. You’ll be joined to the conference and will be able to hear and speak. More detailed help is available here: https://support.google.com/meet/?hl=en#topic=7306097