ContextMenu is activated by right click by default. In order to activate it by left click, you will need to put in some code:
Code: HTML/ASPX
<a href="javascript:void(0)"
onclick="eo_ShowContextMenu(event, 'ContextMenu1')">Show context menu</a>
Note here 'ContextMenu1' is the ID of your context menu. If you are using a server control, for example a Label, you can use the following code to associate it the context menu:
Code: C#
Label1.Attributes["onclick"] = "eo_ShowContextMenu(event, 'ContextMenu1')";
In this case ContextControlID is irrelevant.
Note left click may not always work because a lot of elements have a default action for left click, such as a button, a textbox, ect. Hooking up an onclick handler to those controls would obviously interfere those controls' default behavior.