With Visual Studio 2010 you can crete a sample BCS model that will allow you to create an external list and grab external data to present in SharePoint. Visual Studio has a great template showing you how you can create a sample model that will display all items in the list and then when you cick on one of them – it will open standard SharePoint view item form and show all of the associated details.
However, it’s not entirely apparent how you can create new methods that handle Create, Delete, and Update functions. Here is how to go about it:
1. We’ll open newly created BDC model from solution explorer

2. Then select one of the existing methods on the model, fr example ReadList method that returns a whole list

3. Now you should open BDC explorer. If you don’t see it at the bottom of your VS 2010 screen along with Error List etc – you can open it from View-> Other Windows -> BDC explorer. Now you can see all of the existing methods and you can add a new one depending on the type of the method you need by using the same UI as shwn below:

Once you pick the right method -VS 2010 will create all of the required parameter types for that method. For example, Delete method will get item ID as a parameter; where, Update method will accept your modified Entity.
When you switch back to the code view of your method – you can add any desired functionality to it in a placeholder created:
public static Entity1 Create(Entity1 newEntity1)
{
throw new System.NotImplementedException();
}
That’s it, good luck!