I don't know where to start.

Hey! So I am going to take a introduction of programming next fall (Java language). However, I want to start learning how to program over the summer because I do not want to get a bad grade in my class. I don't know where to start though. I have Mac with Snow Leopard and I do not know where to start. If somebody knows a good website I can go to it would helpful
Thank you.

Check out Thenewboston on YouTube. He has a huge collection of tutorials on Java starting from the very basics :)

The Java™ Tutorials is one of the prime resources to go to. On a mac, the JDK should already be installed (go to the terminal, and type in 'javac -version' to see, javac being the java compiler)

Yes, I agree with copeg. The official Java tutorial website is where you can start to learn the basic of Java and understand the underlying concept. And don't forget to write lots of codes because you can understand better when you write to the code.

You can also Google video lectures from different universities like Harvard CS50. You can follow along with the videos, and try to accomplish the assigned projects as well.