The application owner can control the access permissions of shared users using the Permissions option in the Report Settings. Refer the topic, Access Permissions for more information on configuring the access permissions for users.
When a user adds or modifies a record in his shared application, the name of the user who added/modified the record and the time when it was added/modified will be automatically stored. This information will be displayed in the view, if the columns are selected from Report Settings -> Column Properties option. Refer the topic Display username and time for more information.