How to use <apex:panelGroup>  in Visualforce Page?

<apex:panelGroup> :

A container for multiple child components so that they can be displayed in a single panelGrid cell. An < apex:panelGroup > must be a child component of an < apex:panelGrid >.

This tag supports following attributes:

Attribute	Description
id	An identifier that allows the panelGrid component to be referenced by other components in the page.
layout	The layout style for the panel group. Possible values include "block" (which generates an HTML div tag), "inline" (which generates an HTML span tag), and "none" (which does not generate an HTML tag). If not specified, this value defaults to "inline".
rendered	A Boolean value that specifies whether the component is rendered on the page. If not specified, this value defaults to true.
style	The style used to display the panelGroup component, used primarily for adding inline CSS styles.
styleClass	The style class used to display the panelGroup component, used primarily to designate which CSS styles are applied when using an external CSS stylesheet.

Visualforce Example:

<apex:page >

    <apex:panelGrid columns="3" id="theGrid">

        <apex:outputText value="First" id="theFirst"/>

        <apex:outputText value="Second" id="theSecond"/>

        <apex:panelGroup id="theGroup">

            <apex:outputText value="Third" id="theThird"/>

            <apex:outputText value="Fourth" id="theFourth"/>

        </apex:panelGroup>

    </apex:panelGrid>

</apex:page>