Users allows you to add beta users. The beta environment is a parallel environment that is available to the beta users. These users would then be able to see the two versions of the app namely the one in production environment and one in the beta environment if the App is published in the Beta environment as well. The data submitted to the sheet would also be visible in the respective version of the sheet.
To add a Beta User, simply search and select a Beta user and click Add.
The user gets added as a beta user and can view both versions now. Further, if you choose to Publish App in the Beta environment, then only the Beta users will be able to receive this App update.