MySQL----> Joins

Please explain how to determine what is the left and right table? If you are given data without a table, how are you to determine which side the table is coming from? I was shown a diagram that showed the circles and what was included and what wasn't included. But how do you go from the circles, to the diagram with information, to writing the code that answers questions?

I'm new to relational databases and I think this is the block that prevents me from understanding how to write the code.