Quick answer: That errors tells you that the Java interpreter could not find a main method in your class. Java interpreter needs that method to run your code since it will start running your code from main method.
Long Answer: Even if you make that code work successfully, as far as i see, it will nto do anything. So i recommend you a text based tutorial to start. Start with the following one. It is highly recommended.
Trail: Getting Started (The Java™ Tutorials)