It doesn't. It's a standalone (static) helper method that uses HttpClient to perform the request and feeds the response body into a json parser. It's an extension method [0] which means that there's syntactic sugar so that you can write client.GetFromJsonAsync() and the compiler transforms it into the actual static method call, HttpClientJsonExtensions.GetFromJsonAsync(client).

0: https://learn.microsoft.com/en-us/dotnet/csharp/programming-...