We don't recommend calling any web API function directly from your app. Why? Because you'd have to include the API Key inside your app. The API key is like a password to your account.
So, instead write a script on your website that does whatever you want, then pass whatever information you want to that script on your website. This way the API key is never included in an assembly that's distributed to your end-users.
If you tell me more about what you're trying to accomplish then I'll be able to give you better help.