As a developer how am i supposed to know that i have to use so many methods on a particular object?? example below

what im trying to ask is quite simple, this is a tutorial so i know which methods to use since the teacher is using them, im simply copying them and if explanation is being given im understanding them. BUT i cannot figure out how to know that myself? For example in the video the teacher used this,

Request request = new Request.Builder.url(projectUrl).build;

now as a developer i may have to deal with new APIs for every app, how will i know that i have to create a request object and then use the Builder method on that object and then the url method and give a specific input and then use the build method.

Also, i dont even have an idea about the sequence!, the teacher used the sequence of making a request object and then a call object and then calling the newCall method and then the response method like this:

Request request = new Request.Builder.url(projectUrl).build; Call call = client.newCall(request); Response response = ((Call) call).execute();

bottom line, my question is, how will i know what to do as a developer when theres no teacher to tell me which methods/objects/sequence i should use?