OnInit: Define controls that will be involved with WebPart
CreateChildControls: Control properties and methods previously declared.
OnPreRender: Control’s value kept by ViewState (for example Item value set up by the user to DropDownList nation), is available. For this reason, it’s normal to begin business procedure from here, and in our case we are going to load values for the second dropdown list (Town DropDownList) with the proper data:
Render: For HTML rendering WebPart