I m doing java and knows how to do it but don't konw what to do with it ???

Question

there are always some questions that are meant to be think atleast once !

Answer 1

Think of something you could use and start developing: the more you do, the more you can do. For example you can create your GUI and handle the logic of user interaction to run system commands or use backend programs...
Once you really start using it everything is possible.

Answer 2

fall in love with it and ull find reasons to use it
Android for example ;)