If you wish to build a UI to interact with then I recommend having a look at the Interaction Engine to achieve this, we have a basic UI example scene in 'Tracking Examples' which will help you to get started with this.
If you have an existing user interface built with the U-GUI then we recommend using the UI Input module included in our Preview package in the Unity Plugin. Please see the 'Example UI scene' in Preview Examples for assistance with this.
