Resources tend to be passive content items that are useful for distributing information. They are normally added to the course by a trainer or administrator and then accessed by learners (or other trainers). There are a wide range of different resource types available in Totara Learn such as files, folders, and labels.
You might also want to look at course activities, which are interactive items of content that you can add to a course.
The Totara Academy has a whole course dedicated to using Course resources in Totara Learn. Here you can learn more on how to use various course resources, see best practice, and give it a go yourself.