EDM designer represents your conceptual model. It consists Entities, associations & multiplicity between the entities. Initially it will exactly look like your database table structure but you can add or merge columns or remove columns which are not required by your application from this designer. Even you can add new object in this model which can have columns from different database tables from context menu as shown in above figure. Remember, whatever changes you do here it should be mapped with storage model. So you have to be careful while doing any changes in the designer.