How to use the social media API as a developer?

Question

JavaScript

Let's say I want to manipulate some data on some page from a third-party resource (from some web application, most likely in the Javascript ecosystem ... ), using the API of the social network in question. What does it look like? I would like to look at an example. Of course, the time will come to plunge into the documentation, but first I would like some kind of briefing.