How to add reference of AJAX Control Toolkit in Visual Studio 2012

I am using Visual studio 2012, I want to install Ajax Toolkit in my Project.

From where to get Ajax Toolkit for VS2012? and please explain the steps to add refrence (ajax .dll) into the project.

Also I want to know that what things need to take care when using Ajax Toolkit in Project, both at client and server side.

Thanks in advance.