Create a folder called GBook and store 
the following two files in there.

// Fig. 3.1: GradeBook.java
// Class declaration with one method.

public class GradeBook
{
   // display a welcome message to the GradeBook user
   public void displayMessage()
   {
      System.out.println( "Welcome to the Grade Book!" );
   } // end method displayMessage
} // end class GradeBook

// Fig. 3.2: GradeBookTest.java
// Creating a GradeBook object and calling its displayMessage method.

public class GradeBookTest
{
   // main method begins program execution
   public static void main( String[] args )
   { 
      // create a GradeBook object and assign it to myGradeBook
      GradeBook myGradeBook = new GradeBook(); 

      // call myGradeBook's displayMessage method
      myGradeBook.displayMessage(); 
   } // end main
} // end class GradeBookTest

You compile both files and run the one having main function.
To compile the classes,  type the command

  javac GradeBook.java GradeBookTest.java
or  javac *.java