Follow that step below to help you can collect emails of subscribers.
Step 3 - Navigate to MailChimp for WP > MailChimp then connect with your Mailchimp account you created from step 1 and insert API key then "Save changes"
Step 4 - Create Mailchimp form to collect email.
Navigate to Forms -> Add new form
Import HTML Code below on section Form mark-up Source
<input type="email" name="EMAIL" placeholder="Your email address" required />
<button type="submit" value="subscribe">
Step 5 - After creating your plugin. You must set a position where you want to display.
Open Appearance -> Widgets then drag Mailchimp widget to Newsletter Sidebar. You can bring that sidebar to every position you want. ( You can drag to left, a right sidebar for each page. You can drag to Footer position.... )