Microsoft Silverlight SDK
Microsoft Silverlight SDK is a package that includes the most important libraries required by developers to create Silverlight compatible applications. It is the backbone of every Silverlight implementation and includes the tools required to build and to package the programs.
Enabling creation of Internet and mobile phone applications
The Silverlight framework is designed to help developers create rich Internet applications that can be delivered to the users via Internet browsers such as Internet Explorer, Firefox or Chrome. The framework is a viable solution for developing mobile device apps for the phones that use Windows Phone or Symbian operating systems.
Easily build multimedia content
You can use the components to build applications that support media steaming, graphics and animations as this is the main purpose of the framework. The end user only needs to install the run-time environment in order to use the browser enhancement.
Easy deployment of needed tools
The installer deploys the Silverlight Libraries that include the extensions, the user controls and the server controls. It also includes the Reference Assemblies and the builder components required to prepare the app for use.
Cleverly organized resource libraries
The libraries are organized into folders and use a prefix in order to make them easy to find the tool that you require. For instance the libraries with the System.Windows.Controls prefix are designed to create new controls which enable the user to communicate with the interface.
This software development kit allows you to start creating your Silverlight programs. You have to choose if you want to use a simple text editor to write the code or to use a professional tool such as Visual Studio.
To sum it up
All in all, Microsoft Silverlight SDK is a package that contains nearly anything you need to develop Silverlight applications. However, beginners might have a difficult time, as it is mainly addressed to those with a little bit more coding knowledge that just the basics.