Debugging means trying to find the mistakes you have made. This can be difficut or frustrating. Here's a discussion:
There are two kinds of errors when programming in Java. There are compile time errors which happen when you compile the program using the javac command, and run time errors when you run the program using the java command.
Mistakes in your program which make these errors happen are called bugs, and the detective work needed to find them is called debugging. It is a rule of life that all programmers suffer from bugs. Your aim should be not to let them slow you down too much.