Hi Lawrence,
Thanks for reaching out and thanks for using Crio Pro WordPress theme!
There a few different ways to add third party code to Crio. You can create a custom HTML block inside of the page editor to add HTML, then use the CSS/JS Editor inside of the WordPress Customizer to style your content with CSS.
The best way to go about adding new template files would be to download and install a plugin like Code Snippets and add your code there. That way you can easily keep track of your template files and reuse them on multiple pages and posts types.
I hope this helps. Please reach back out if you have any other questions for us.