There are a lot of tools to help make building apps easier. To help familiarize yourself with some of the things that the tools can help with, here are some places to start:
A simple app that takes a remote resource containing some metadata and displays it to the user so they can easily download new torrents.
A more advanced tutorial, for apps that need access to all of the torrents being downloaded by a client.
Lots of µTorrent users use languages other than english. This tutorial shows you how to make your app localizable.
This tutorial covers the implementation of a torrent search interface in the µTorrent client applying XML results to an HTML view template.
All tutorials also come with completed example applications. If you’d like to take a look at any of these, check out the Examples Directory.