Create subscription forms in word press

Can I know how to create subscription forms (also known as opt in form) in word press? For instance, I want to set up a website (using word press) with some opt-in-form so as to collect client database. The client database will be transfer to an autoresponder email (eg Imnica mail) so that I can send future emails to my list to inform them of further products and services.

Please assist. Thanks.