To fix the error, use Notepad to fix the source file.
Usually you will have two windows open on your computer: one for Notepad (or other editor) and one for the command interpreter.
To fix the syntax error,
change the "C" to a "c" and save the file.
Now use  javac  to compile the source file,
and if there are no errors, use  java  to
run it.
If you forget to save the file after making the change,
and then enter the command  javac Hello.java,
what will happen?