Show Status message on Page using apex:actionStatus component.

<apex:page >
  <apex:form id="frmId">
     <apex:pageBlock >
        <apex:commandButton value="Save!" status="statusid" reRender="frmId"/>
       
<apex:actionstatus id="statusid">
            <apex:facet name="start">
                <div class="waitingSearchDiv" id="el_loading" style="background-color: #fbfbfb;height: 100%;opacity:0.65;width:100%;"> 
                    <div class="waitingHolder" style="top: 74.2px; width: 91px;">
                        <img class="waitingImage" src="/img/loading.gif" title="Please Wait..." />
                        <span class="waitingDescription">Please Wait...</span>
                    </div>
                </div>
            </apex:facet>
        </apex:actionstatus>

     </apex:pageBlock>
  </apex:form>
</apex:page>

apex:actionStatus visualforce component is used to show message on  the page when server is busy.

It stop the status message once request completed.