To create a form go to Mailchimp > Form and create a form, after that paste the following markup into the editing window.
<div class='mailchimp-subscribe-form'>
<div>
<input type="email" name="EMAIL" placeholder="Your email address" required />
<button type="submit"><span>Sign Up</span><i></i></button>
</div>
<div>
<input name="AGREE_TO_TERMS" type="checkbox" value="1" required="">
By checking this box, you confirm that you have read and are agreeingto our
terms of use regarding the storage of the data submitted throughthis form.</div></div>