Every file that you upload into a Moodle course, is stored in a Moodle repository. Before you add files to our course, you need to understand how repositories work and how to choose the right kind for your course.
A repository is a storage area that Moodle can access. The repository doesn't need to be on your server. It just needs to be accessible to your Moodle system.
You can enable it from
Site administration → Plugins → Repository → Manage repositories
Use server files when you want to re-use a file that you uploaded into another course. For example, you want to re-use a graphic that you added to a page in another course, or a document that you added to another course.
Upload a file
The file that you want to add to your course resides on your computer, and you want to use it in the current course. The file must be no larger than the upload limit for your Moodle system.
The file that you want to use has been uploaded to the Moodle data directory. You usually do this when the file is too big to upload directly into Moodle, or, when you need to upload a lot of files all at once.
Dropbox, Google Drive, Amazon S3, OneDrive
When you want to use a service outside of Moodle to store your files.
Flickr, Picasa Web Album
When you want to use photos that are part of an online album.