A good think about how you would exchange letters can solve this code as they've just given you the most simple example.

You could read through a few ebooks available on cyptography freely on the internet, but you don't even need to do that in this case, I could just tell you.

The most common letter used in the english language is 'e'. Now identify the dot pattern that is the most common. Voila, you can translate a lot of the code. For the other letters, I would investigate some sort of chart that ranks the most common letters in the English alphabet. With a bit of playing you can do this with a pencil and paper.

Obviously computer cryptography is more advanced, but your question related to this code specifically.