I have  a custom object Purchase Order which has a child object Purchase Order lines.
The purchase order lines have a Product lookup field(product__c) and a quantity  field(quantity__c).

Now i need to have  a list button "Create Prod Serials" on the purchase order lines which does the following:

1)First page:Displays the selected purchase order lines as a datatable displaying the product and the  input quantity field  (if the user wants to edit the quantity).This page has a button "Confirm".

2)When the "Confirm" button is clicked,
**the controller should first save the changes made,
**then for example the quantity is 2 on a line ,it should create 2 asset records for the product passing the product field value to the asset fields :name&product.
**display the newly created asset records as a data table with the product serial as input field.This  has a save button that saves the records



Iam a total newbie to controllers and though i have been reading on this ,its still very confusing and iam not able to execute this logic.

I tried by creating a custom list button "Create Serial No.s" on the purchase order lines which calls a visualforce page.
I created a simple visualforce page   that displays the selected purchase order line fields as a data table.

The visualforce page is as below:

<apex:page standardController="Purchase_Order_Line__c" >

    <apex:form >
        <apex:pageBlock >
            <apex:pageBlockButtons location="Bottom"><apex:commandButton action="{!save}" value="Save"/>
                        </apex:pageBlockButtons>
            <apex:pageBlockTable value="{!selected}" var="line"  border="1">
            <tr>
    <td><apex:column value="{!line.name}" style="white-space:nowrap ;font-weight:bold"/></td>
        </tr>
        <apex:column />
   <apex:column value="{!line.Product__c}"/>
   <apex:column headerValue="Purchase Quantity">
   <apex:inputField value="{!line.Quantity__c}"/>
   </apex:column>             
            </apex:pageBlockTable>
        </apex:pageBlock>

    </apex:form>
</apex:page>



Now to achieve my logic i think i should use a controller extension that has the save ,create and display methods.


Public class myextension{

Page reference save(){

}


public create asset(){
}


public display asset(){
}


}

I tried writing some code but iam really struggling with the navigation ...

Please help me with this controller extension .i need to learn how to do this...