Adding a variable to my form

I’m not claiming to be a developer but can cobble together a fairly decent site using WP and ACF. I’m just struggling to get my head round how to actually use this extension.

For instance I have a variable called $refer_title in my page. The same page that contains the CF7 form. How do I use this plugin extension to send this variable as part of the form?

I keep seeing references to more short-codes, do I first need to create a shortcode out of the variable?