From Gmail:

1. In the sidebar, click Start a meeting.
2. Click Join now for a video meeting, or click Join and use a phone for audio for an audio-only meeting.

From Calendar:

1. Click Create .                
2. Add your event details and guests.
3. Click Add rooms, location, or conferencing. 
4. Click Save.

From Gmail:

In the sidebar, click Join a meeting and enter a meeting code.

From Calendar:

Click the event, then click Join Hangouts Meet.

From Meet:

Join a scheduled meeting or use a meeting code.

From mobile devices:

Open the Android or Apple® iOS® Meet app.