How use viewModels + Entity Framework? Is necessary add a migration?

I am using asp.net mvc 4 + entity framework and for the first time I'm using ViewModels. I'm reading this tutorial: http://ift.tt/1DYBwYe

After step in that it creates classes viewmodel, he's going to create the controller, but does not explain whether to create a migration to add these classes in the bank, it is necessary?

For I'm creating a migration like this:

add-migration xxx

But when the migration is created, the methods of up () and down () are coming empty, can anyone help me?