1. Select the page layout by clicking on the Page Layout picklist at the top left.

2. In the 'Properties for Page' pane at the right, select the 'Event Type' as 'Webservice' for the required event (On Load, Before Save/Insert, Before Save/Update, After Save/Insert, or After Save/Update).

3. In the 'Method' text box, enter the Apex web service name as ClassName.MethodName (for example, SVMXC__INTF_WebServicesDef.INTF_WORD_USG_GetPrice_WS).