Your first step would be to read the requirements to find out what "registered" means. If they don't say, then go and ask somebody what it means.
Second step would be to implement that in code. Now at the moment none of us knows what it means (except maybe you) so none of use can write any code.
> Actually i need to check the user is register or not.
Ah, I see. That means that you are the one responsible for the design too? Well, you need to keep a list of registered users somewhere. Preferably somewhere outside the application. Does that give you any ideas?
But if you have to ask this question, I would suggest you should go away and get some basic experience in computer systems before attempting this. Beginners should not be designing things related to computer security.