Confirm data is being collected in Analytics
Once you've implemented the SDK for your app (iOS | Android) or implemented the global site tag for your website, Analytics starts sending data to your property within minutes (usually 10-15 minutes).
To confirm that your property is receiving data, check the Realtime report. If you've set up your measurement code correctly, the Users right now card should refresh about every 15 seconds with a new count of users.
It takes 24-48 hours for Analytics to process the data for the other reports.
To validate your configuration for mobile devices during development, you can use DebugView.