Visualforce Page:
<apex:page> <apex:form> <apex:pageblock> <apex:pageblocksection title="Confirm dialog box Demo" collapsible="false"> <apex:commandbutton value="Click to Confirm" onclick="return confirm('Do you want to submit');"></apex:commandbutton> </apex:pageblocksection> </apex:pageblock> </apex:form> </apex:page>