How to create a custom email signup form?

I'm using jquery blockui to show a newsletter modal on frontpage and I already have the form, so I need to know how to insert that email as a new subscriber in WP, I mean, what is the php code to make the insertion properly?

I will need to get the response using ajax (the code should be return "done" or "failed" or some stuff like that.

Any help?

via Chebli Mohamed