The display shows energy metering information, either for the current charging session or for the total lifetime of the charger.
From left to right and top to bottom you see: a charging indicator that shows whether a car is charging; the measured energy, or an error code when there is an error; the label Session or Total, which tells you whether the number is the energy of the current session or the total energy the charger has delivered; and the unit of measurement, kWh.
You can find the full description in the user manual on the downloads page.