Meet Hour Google Workspace Addon for Gmail and Calendar.

Once the Addon is installed.

For Gmail -> Click on Compose -> Later tap on Meet Hour icon on Compose wndow -> Click Login and Tap on Instant Meeting to Automatically print the meeting details in your compose body.

For Calendar -> Click a New Event -> More options -> Select from the dropdown "Add Video Conference". There you will find Meet Hour. 
Select Meet Hour -> Authorize yourself and login in Meet Hour to create an Instant Meeting.

 This helps to create instant meeing