The Autodesk Revit API requires the Microsoft .NET Framework v4.5. To edit and debug your API applications, you need an interactive development environment such as Microsoft Visual Studio 2012 Professional or one of the MS Visual Studio Express Editions for C# or Visual Basic.NET. (Visual Studio Professional is recommended, as Express editions do not support DLL debugging.) When developing with the Autodesk Revit API, ensure that your project references two DLLs: RevitAPI.dll and RevitAPIUI.dll contained in the Autodesk Revit Program directory.
Some programming skills are required to effectively use the API. If you are a beginner in programming, we strongly advise you to learn Microsoft Visual Studio 2012 and one of the compatible languages like C# or Visual Basic.NET. There are many good books and classes to get you started.
Resources:
Online resources
Books: