To be able to create tables using model-first development, you have to have a Relational Model Data storage container in the project for a given database type. To do so, right click the 'Relational Model Data' node in the Project Explorer or Catalog Explorer and select Add Relational Model Data Storage for a Database from the context menu. In the dialog, select the database you want to use in your project. Keep in mind that DDL SQL scripts aren't supported on MS Access, so choose a database other than MS Access.
A new storage container is added to the project and immediately visible in both Project Explorer and Catalog Explorer below the Relational Model Data node.
When a relational model data container is added, the sync mode of its elements is set automatically to the source 'Model' as an empty relational model data container is used mainly for model first development.