How to call server side method in 365.js office files

I am playing around with Office 365 API applications and where can I find documentation for the office api to select specific rows and values ​​(s) of cell (s) / to select a specific sheet from all sheets pragmatically in a .js file.

I am using the following code to call inside a function

ServerClass

- this is the class present in the ServerClass.cs

file Call

- this is the name of the function

$.ajax({
            url: "ServerClass/Call", success: function () {
                debugger;
            }
        });

public class ServerClass
    {
        [WebMethod] 
        public static void Call()
        { }
    }