Mini-B USB Jack is where you connect the USB cable to yor computer
D2-D12 are the digital pins (Input/Output). In the experiments are mentioned as D(number).
A1-A7 are the analog pins (Input/Output). In the experiments are mentioned as A(number).
GND is the Ground pin.
5V is the 5 Volts pin.
3V3 is the 3.3 Volts pin.
All the other pins are normally not used in this kit, in any case this page should be considered the main reference page when you need to use the microcontroller with your own experiments.
This picture uses abstract, graphic symbols rather than the previous realistic picture.