How do I make a mailing list entry form

1

I am in the dark on this, and very stressed for time, I basically dont have time to figure it out right now given the massive work load due later today so any help will be really appreciated. All I really need is a push in the right direction. It jus needs to be a box where they can enter their email and a button that allows them to send it to my clients email. I also need to have the text in the original box say something. please help?