<apex:page controller="AccContact">
  <apex:form >
  <apex:pageBlock >
  <apex:pageBlockTable value="{!acclst}" var="a">
  
 <apex:column headerValue="Name">
  <apex:commandLink action="{!selacc}">
  <apex:param name="conlst" value="{!a.id}"/>
  <apex:outputText value="{!a.name}"/>
  </apex:commandlink>
  </apex:column>
  <!--accounts-->
   </apex:pageBlockTable>
    <apex:pageBlockTable value="{!accconts1}" var="a">
    <apex:column headerValue="AccountName" value="{!a.Name}"/>
    <!--contacts-->
    <apex:column headerValue="list contacts">
   <apex:pageBlockTable value="{!a.contacts}" var="c">
  <apex:column headerValue="ContactName">
  <apex:outputText value="{!c.lastname}"></apex:outputText>
  </apex:column>
  <!--opportunities-->
  <apex:column headerValue="Opportunity list">
  <apex:pageBlockTable value="{!a.opportunities}" var="p">
  <apex:column headerValue="Opportunity Name">
  <apex:outputText value="{!p.name}">
  </apex:outputText>
  </apex:column>
  </apex:pageBlockTable><!-- End opportunity-->
  </apex:column>
 </apex:pageBlockTable><!-- End contact-->
 </apex:column>
 </apex:pageBlockTable><!--end account-->
  </apex:pageBlock>
  </apex:form>
</apex:page>

public with sharing class AccContact {

    public list<contact> conlst { get; set; }

   // public contact c { get; set; }
   /* public  void getSelacc() {
    }*/

    public list<account> accconts1 { get; set; }

    public PageReference selacc() {
    string getid=apexpages.currentpage().getparameters().get('conlst');
         accconts1=[select id,name,(select id,lastname from contacts) ,(select name from Opportunities ) from account where id=:getid ];
            system.debug(accconts1);
      return null;
    }


    public List<Account> acclst { get; set; }
   public  AccContact (){
     acclst=[select id,name  from account ];
     system.debug(acclst);
   
   }
}