You need to create new form go to WP > forms > Add new
Type a title. then click on Add element.
select here your element for subscription form.
Type name of element without space. only underscore_ is allowed. then Type your text in Placeholder. scroll down and check if you make it required. then hit save.
Here you can set columns for the element.
I have two fields for the form. email and submit button.
Right below the form section you can see the settings. make sure use form action as mailchimp.
Then in the form > settings here you have all the settings for the form to set pages and for subcription mailchimp info fill these field correctly.
Then click on forms. copy the form Id “digits” only
then go to wp > PostAds Options > theme settings > footer
Past in form ID field. Place your mailchimp id right below field.
Its done.Hope this tutorial helps you.Good Luck !