AutoMapper is a simple little library built to solve a deceptively complex problem - getting rid of code that mapped one object to another. This type of code is rather dreary and boring to write, so why not invent a tool to do it for us?
Check out the getting started guide. When you're done there, the wiki goes in to the nitty-gritty details. Finally, check out the dnrTV episode for a full walkthrough. If you have questions, you can post them to the Mailing List.
First, install NuGet. Then, install AutoMapper from the package manager console:
PM> Install-Package AutoMapper