Dynamic Render:

Dynamic Render:
This is a simple rendering of detail record of that you selected.Here action support function is main since it refreshed by the server when a particular event occurs.
Here is the controller

public with sharing class DynamicDetail
{
    public String chosenAccountId {get; set;}
    public List<SelectOption> getAccounts()
    {
        List<SelectOption> accOptions=new List<SelectOption>();
        accOptions.add(new SelectOption('Choose', 'Choose'));
        for (Account acc : [select id, Name from Account ])
        {
            accOptions.add(new SelectOption(acc.id, acc.Name));
        }
       
        return accOptions;
    }
}
and the page looks like this

<apex:page controller="DynamicDetail" tabstyle="Account" sidebar="false">
  <apex:form >
    <apex:pageblock title="Choose Account">
       <apex:pageBlockSection >
         <apex:selectList value="{!chosenAccountId}" size="1">
           <apex:selectOptions value="{!accounts}" />
           <apex:actionSupport event="onchange" rerender="detail" status="detailstatus"/>
         </apex:selectList>
       </apex:pageBlockSection>
    </apex:pageblock>
   
    <apex:pageBlock title="Account Preview">
      <apex:actionStatus id="detailstatus">
        <apex:facet name="start">
          <apex:outputText value="Please wait ..."/>
        </apex:facet>
        <apex:facet name="stop">
          <apex:outputPanel id="detail">
            <apex:detail subject="{!chosenAccountId}" rendered="{!NOT(ISBLANK(chosenAccountId))}"
                        relatedList="false"/>
          </apex:outputPanel>
        </apex:facet>
      </apex:actionStatus>
    </apex:pageBlock>
   
  </apex:form>
 </apex:page>