Adding a working newsletter registration form to Uncode is really simple and you just need to install a free addon. In last section before the footer it's possible to browse an example of newsletter registration form:
Uncode forms are based on Contact Form 7, this is the most popular WordPress contact form plugin and it's also one of the optional plugins packed with the theme. To extend the functionalities of this plugin and enable the newsletter registration functionality, you just need to install the official MailChimp addon:
This is a super-fast tool that lets you build beautiful looking MailChimp forms to maximize conversions and grow your mailing list. If you don't use MailChimp, in the WordPress official plugins repository, you can find dedicated free addons like MailChimp Forms by Optin Cat.