Real Time tab is a place where you can track your Google Analytics Real Time data.
You can use Real time tab as a TV dashboard to track your data in real time, especially if you have just launched a specific campaign and you want to see how it behaves.
IMPORTANT NOTE: Widgets from your dashboard won't be automatically copied to your Daily Tab within that dashboard. If you want to track certain metrics in real-time, you need to go to the Daily Tab of that dashboard and add them manually, as you would regular widgets within your dashboard.
More information on setting up Daily Tab available here: What is Daily tab on my Dashboard?