You can upload files to your personal account. These files will only be accessible to you and can be reused in other areas of the site.
Step 1: On your Dashboard, scroll down and click on "Manage Personal Cloud..."
Step 2: Here you can (1) select your preferred page view, (2) access the file picker, create new folders, or (3) drag and drop files to upload to your personal cloud.
Once you're happy, click "Save changes." Your private files will now be accessible within your personal cloud - which will be available as a source within the "File picker" when selecting files to use within a course.