SFDC Coding Start Up:-

Hi Friends,

  This is very useful for Developers who is very new to Coding.

How To create a Visual force Page/Apex class :-

YourName-->Setup --> App Setup --> Develop --> Pages/ Apex classes --> Name of that page

(OR)

Go with the URL 

ap1.salesforce.com/apex/ExamplePage

Then after If you want to see your output..:-

You should go Using URL only

Types of Controllers:-

Standardcontroller :- StandardController objects reference the pre-built Visualforce

                                controllers provided by salesforce.com.

Controller :-             A custom controller is an Apex class that implements all of the logic for

                                a page without  leveraging a standard controller. 

Extension controller :- A controller extension is an Apex class that extends the functionality

                                  of a standard or custom controller.

Using Standard Controller:-

Here We have a scenario , i.e Save a record using VF page.

<apex:page standardController="Account">
    <apex:form >
        <apex:pageBlock title="My Content" mode="edit">
            <apex:pageBlockButtons >
                <apex:commandButton action="{!save}" value="Save"/>
                <apex:commandButton action="{!cancel}" value="cancel"/>
            </apex:pageBlockButtons>
            <apex:pageBlockSection title="My Content Section" columns="2">
                <apex:inputField value="{!account.name}"/>
                <apex:inputField value="{!account.ParentPickList__c}"/>
                <apex:inputField value="{!account.type}"/>
                <apex:inputField value="{!account.AccountNumber}"/>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>

Using Controller:-

so here is the simple code for Calculator . I am using Controller with Action methods.

<apex:page controller="calculator">

    <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 Result :<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 calculator
{

    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;
 }
 
}

Using Extension  Controller:-

so here is the simple code for Saving record. Please note that I've used standard controller
("Account" in the code) Instead of save Button I am using My Logic for saving the record.

<apex:page standardController="Account" extensions="MyOwnLogic">
    <apex:form >
        <apex:pageBlock title="My Content" mode="edit">
            <apex:pageBlockButtons >
                 <apex:commandButton action="{!Logic}" value="MyLogic"/>
                <apex:commandButton action="{!Cancel}" value="Cancel">
                </apex:commandButton>
            </apex:pageBlockButtons>
            <apex:pageBlockSection title="My Content Section" columns="2">
                <apex:inputField value="{!account.name}"/>
                <apex:inputField value="{!account.site}"/>
                <apex:inputField value="{!account.type}"/>
                <apex:inputField value="{!account.accountNumber}"/>
                 <apex:inputField value="{!account.ParentID}"/>
                 <apex:inputField value="{!account.SLASerialNumber__c}"/>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>

public class MyOwnLogic {

    Account AccRec;
    String VarStr;
    public MyOwnLogic(ApexPages.StandardController abc) 
    {
        AccRec=(Account)abc.getRecord();
        
    }
    public void Logic()
    {
        System.debug('Account Values---------->'+AccRec.name);
        VarStr=ApexPages.currentPage().getParameters().get('txt');
        system.debug('URL VALUE------------->'+VarStr);
        upsert AccRec;
    }

}