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 email 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
<p><i class="fa fa-envelope"></i><input type="email" name="EMAIL" placeholder="Your email address" required /></p><button type="submit" class="btn">Subscribe</button>
Step 5 - After creating from of your plugin. You must set position where you want to display.
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.... )