Forget about importing class Teacher. You don't need to do that if both class Teacher and TestTeacher are in the same package (which they most likely are for your assignment).
Make sure Teacher.java and TestTeacher.java are in the same directory.
Are you using JCreator, or are you doing this on the command line with a simple text editor? If you're compiling the classes manually, then make sure that the CLASSPATH environment variable is
not set (or make sure that the current directory is included in the classpath). In a command prompt window, try compiling the classes with commands like these:
javac -cp . Teacher.java
javac -cp . TestTeacher.java
And then try to run it with:
java -cp . TestTeacher
Note: the
-cp . will set the classpath to the current directory "."