This tells Rails to update the database to include a table for our new model.
rake (ruby make) is a tool that allows you to run small Ruby programs (tasks) that you use often in your application.
Here, rake db:migrate is a task provided by the Rails framework. It uses the migration file we just created (db/migrate/201xxxxxxxxxxx_create_topics.rb) to change the database. Database migration files can be crucial to code collaboration.
You can run rake -T to see a list of all the rake commands your app currently responds to, along with a short description of each task.