This section contains the documentation for Unity 2D.
You can read about how to change the 2D/3D mode and find more detail about how the modes differ here: 2D and 3D Mode Settings.
See 2D or 3D Projects for information on working in 2D or 3D.
Is something described here not working as you expect it to? It might be a Known Issue. Please check with the Issue Tracker at issuetracker.unity3d.com.