Read about the Arduino Ethernet library and the Aduino Ethernet shield.
The exercise must be done in groups of three because we have only very few Ethernet shields.
It should be safe to use IP numbers from 152.18.69.201 to 152.18.69.205 in this exercise.
The Arduino Ethernet library is buggy. Try following the directions for installing the Ethernet2 library into your Arudino directory. This does not working flawlessly, but it does work much better.
If you are really ambitious, look at the code for the Ethernet library and try to fix the bugs.
Your task is to write a program that uses the Arduino send and receive Ethernet packets.
For a "C", receive or send at least one byte.
For a "B-", receive and send at least one byte.
For a "B+", do some non-trivial data interchange, such as, reading a web page.
For an "A", write a Arudino program along with a Processing or Python program that does some interesting interaction.