We are using MailChimp for WP plugin for Newsletter subscribe. You can read more about MailChimp from here
Follow that step below to help you can collect emails of subscribers.
Step 1 - Signup for Mailchimp account then create your lists to collect email .
Step 2 - Install and active plugin MailChimp for WP .
Step 3 - Navigate to MailChimp for WP > MailChimp then connect with your mailchimp account you created from step 1 .
Step 4 - Create mailchimp form to collect email. Navigate to Forms
Import HTML Code below on section Form mark-up Source
Source :
<div class="mc4wp-form-group">
<input type="email" name="EMAIL" placeholder="Your Email" required />
<span class="fa fa-envelope-o mc4wp-form-control-feedback" aria-hidden="true"></span>
<button type="submit" value="Submit">
Going Appearance -> Widgets then drag mailchimp widget to Newsletter Sidebar. You can bring that sidebar to every position you want. ( You can drag to left, right sidebar for each page. You can drag to Footer position.... )