How to check duplicate email? noob question.

[eluser]anna16[/eluser]
Hi people

Sorry this is noob question.

For example i have a form.
Let say it has an email input field.
I want to get the value of that email and compare
it into the existing database.

It should check the duplicate of this email.
And should display an error message if the duplicate email is found.

Can you show me the controller, model and view.
Or a short example codes for this.
Sorry I'm a beginner.

Thanks in advance.