When you are designing database for an application, there can be 3 core levels at which you can design your database.
1. Conceptual Level: At this level you are only aware of high level entities and their relationships. For example you know that you have “Employee” Entity who “works for” a “Department” and “has” an “Address”. You are not worried about details.
2. Logical Level: You try to add as much details as possible, without worrying about how it will actually be converted to a physical database structure. So will provide any attributes for “Employee” i.e. Id, FirstName, LastName, AddressId, Salary and define primary and foreign key relations.
3. Physical Level: This is the actual representation of your database design with exact column names, types etc.