Creating a basic Item Event Handler

Scenario:
You want to write an event handler to cancel the deletion of an item from Announcement List ( Type = 104 )

Event Handler Code:

using Microsoft.SharePoint;

namespace TrainingSamples
{
    public class DeletingAction : SPItemEventReceiver{
      public override void ItemDeleting(SPItemEventProperties properties){
        properties.Cancel = true;
        properties.ErrorMessage = "Deleting items from " + properties.RelativeWebUrl + " is not supported.";
      }
   }
}

Feature.xml

<Feature Scope="Web"
   Title="Deleting Event Handler"
   Id="GUID"
   xmlns="http://schemas.microsoft.com/sharepoint/">
   <ElementManifests>
      <ElementManifest Location="Elements.xml"/>
   </ElementManifests>
</Feature>

Elements.xml:

<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
   <Receivers ListTemplateId="104">
      <Receiver>
         <Name>DeletingEventHandler</Name>
         <Type>ItemDeleting</Type>
         <SequenceNumber>10000</SequenceNumber>
         <Assembly>DeletingEventHandler, Version=1.0.0.0, Culture=neutral, PublicKeyToken=a26b5449ac4a4cf3</Assembly>
         <Class>DeletingEventHandler.DeletingAction</Class>
         <Data></Data>
         <Filter></Filter>
      </Receiver>
   </Receivers>
</Elements>

Additional Notes:
This will attach event handler to any list of Type=104. So If you have specific requirements to attach event handler to a particular list only, then go for a Feature Receiver.