A datalogger is a particular mounting which is able to registered some values on a support ( like SD card ) periodically. In other words, a measure, represented by a value, is realised every N second.
So this system can be used in many projects that need a measurement every N second and that have to record it on a non-volatile memory ( for meteorologist this type of system can be used to make probe like hygrometer or thermometer ).
When you plug your SD card into a computer, a excel file nammed Light is created and all the value of the analog reading appears in a column nammed Brightness value per seconds.
There are no connections to make between the Arduino UNO and the Datalogger Shield, you only have to plug the datalogger shield on the Arduino UNO.
The code of this project registered on the card the brightness per seconds. The values come from a photoresistor so connections are really simple.