Call page with get parameter, on that page load pull data

Until now I’ve only needed to use the logged in users info from the security provider to filter data. Now I have a repeating table and when you click on an item i need to call the detail page, passing that parameter to it. I have the query param defined on the detail page and I can pass a value using that parameter from the referring page.

For the life of me I cannot figure out how to use that parameter in a server connect API to get back the detail.
I’ve read about $_PARAMS, library, and API, but none of it tells me how to use this GET parameter on a page and pass it to a server connect to query and return what i need to the page.

Or i’m really tired and have completely overlooked it.