Total = Application + Data
Application = Size of APK file of the app
Data = Space consumed by
/data/data/<Package_Name_of_App> (it contains data stored by the app)
Other stats details:
Force Stop button is active, it means the app is running in background. You can use this button to stop the app from running.
Cache section shows how much data the app has stored in
Clear Defaults button is active, it means the app is set as default to complete an action like sending email, open URL etc. You can tap this button to clear default(s).
On the same page, you can get list & small description about
Permissions the app has. If you need explanation of Permissions, check this article out.