You can find the client-side API reference for all the controls here. In the Table of Contents, navigate to the 'Controls' item and select a control. Most controls have a 'Client-Side Programming' option, which contains details about the client-side API and examples of how to use it.
Also, this Help documentation is available on your computer as well. It is installed when into your Telerik installation folder when you install the RadControls.
I hope that helps. If you have any further questions, please let me know.