Here is an example for your requirement.

<apex:page controller="TestPage4">
  
  <apex:form >
      <apex:pageBlock id="block">
          <apex:pageBlockSection title="Section 1" rendered="{!showSection1}">
          
          </apex:pageBlockSection>
          <apex:pageBlockSection title="Section 2" rendered="{!showSection2}">
          
          </apex:pageBlockSection>
          <apex:pageBlockSection title="Section 3" rendered="{!showSection3}">
          
          </apex:pageBlockSection>
      </apex:pageBlock>
      
      <apex:commandButton action="{!method1}" value="Button1" reRender="block"/>
      <apex:commandButton action="{!method2}" value="Button2" reRender="block"/>
  </apex:form>
</apex:page>

public with sharing class TestPage4 {
    public Boolean showSection1{get;set;}
     public Boolean showSection2{get;set;}
     public Boolean showSection3{get;set;}
     
     public TestPage4 ()
     {
         showSection1= false;
        showSection2= true;
        showSection3 = true;
     }

    public PageReference method2() {
       showSection1= true;
        showSection2= false;
        showSection3 = true;
        return null;
    }


    public PageReference method1() {
        showSection1= false;
        showSection2= true;
        showSection3 = false;
        return null;
    }

}

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