To have newsletter form as shown on demo on other pages, you need to be technically sound on WordPress.
-> You can find the seperate section for newsletter form on template-hompepage.php, then you can copy those code and paste it on specific template you want. For an example for single page you need to paste on page.php whereas for signle post single.php…
-> Another way is to take help from plugin. You can use mailchimp plugin for newletter subscriber. After creating form on mailchimp you can use the shortcode on to footersidebar.
Note: This won’t give the design same as the design shown on demo.