Try to do small programs first , like Addion then Understand Step by Step process

What is SET,GET, Action methods, how they perform, like that you can follow up

simple program for you

<apex:page controller="Addition">
    <apex:form >
       <apex:pageBlock >
         Enter Va1ue1: <apex:inputText value="{!Value1}"/>
          Enter Value2: <apex:inputText value="{!Value2}"/><br/>
          Value1OutPut:<apex:OutputText value="{!Value1}"/><br/>
          Value2OutPut:<apex:OutputText value="{!Value2}"/><br/>
          Your Addtion Value :<apex:outputText value="{!OutputValue}"/>
           <apex:pageBlockButtons >
               <apex:commandButton value="Add" action="{!Add}"/>
               <apex:commandButton value="Sub" action="{!Sub}"/>
               <apex:commandButton value="Mul" action="{!Mul}"/>
               <apex:commandButton value="Div" action="{!Div}"/>
           </apex:pageBlockButtons>
       </apex:pageBlock>
    </apex:form>
</apex:page>

public class Addition
{

    public String getNum1() {
        return null;
    }

 Integer num1,num2,num3;
 
 public Void SetValue1(Integer v1)
 {
     num1=v1;
 }  
 public Integer getValue1()
 {
     return num1;
 }  
 public void SetValue2(Integer v2)
 {
     num2=v2;
 }
 public Integer getValue2()
 {
     return num2;
 }
 public Integer getOutputValue()
 {
      return num3;
 }
 public void Add()
 {
     system.debug('<------------METHOD IS CALLING---------->');
     num3=num1+num2;
 }
  public void Sub()
 {
     system.debug('<------------METHOD IS CALLING---------->');
     num3=num1-num2;
 }
  public void Mul()
 {
     system.debug('<------------METHOD IS CALLING---------->');
     num3=num1*num2;
 }
  public void Div()
 {
     system.debug('<------------METHOD IS CALLING---------->');
     num3=num1/num2;
 }
 
}

If it is helpful plz make it as solution for others it may benfit

Prem