How are your running your application? Are you talking about in debug / testing mode using runserver, or are you talking about in a production mode?
The two answers are different.
In a test/debug mode, there are settings file settings that need to be set -
see the static-files how-to page.
In a production environment, you may want the static files served by your webserver (Nginx / Apache). If your settings are correct, you would use the “collectstatic” management command to copy those files to the directory from which they can be served.
Just as an addendum to the excellent answer by Ken: If you don’t want to have to deal with static files configurations in production, take a look at whitenoise.