Connect to API via jQuery & Ajax in Sage 9

I’ve been building a website,
On one of my pages, the manager asked me to build it with jQuery (and Ajax) to avoid requesting the server more and more when people click on different tabs, basically make it more user-friendly with JS.
I don’t have much experience with Sage, nor with jQuery or Ajax, but since I know JS, those latter two are easier.
What are the exact steps needed to be done to make the WP API accessible with jQuery and Ajax, what files should I modify? What functions should I introduce? Any tip is greatly appreciated. I tried many ways written on the web (for WP not Sage), none works so far, so I came here.
By the way I know how to do REST API, but that does not help me as some plugins (ACF) and taxonomies are related to the posts that I want to see, so the best way is to use WP API through jQuery and AJAX.
Any help is apprecited.

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