While all Web Services follow the same standards, they all do different things. They wouldn't be worth anything if you didn't get the information you need, or if they contained a lot of excess data. If you are unfamiliar with a particular Web Service, there are a few things that you can do to figure out what data is available and how to get it.
Note: web services sometimes take a lot of time to return results, especially the first time they are called. If you put your Web Services script in a button, the client will freeze until the call is complete (this is because the event handlers are run on the GUI thread). It's a good idea to use system.util.invokeAsynchronous() or add a waiting image to your screen to let the user know Ignition is working as expected.
See Overview & Simple Arguments to get started.