The generate command produces a migration to create a microposts table in the database. The biggest difference is the use of references, which automatically adds a user_id column (along with an index and a foreign key reference) for use in the user/micropost association. As with the User model, the Micropost model migration automatically includes the t.timestamps line, which adds the magic created_at and updated_at columns.
rails generate model Micropost content:text user:references