By default, complete courses are not downloadable from a computer. We do this out of concerns for piracy. We do allow instructors to enable downloading of their lectures, however, if they wish.
Please note that you can always save courses for offline viewing on the Udemy mobile app (see below). Practice activities like quizzes and practice tests, etc. cannot be downloaded and completed offline.
Downloading a Lecture
To see if an instructor has enabled downloading for a lecture, move your cursor to the gear icon at the bottom right of the lecture player. If Download lecture is not grayed out, then you will be able to download it to your computer, by clicking on those two words.
Please note that the quality resolution of the downloaded video, will match the quality you had set, when you were viewing the course at Udemy.com. For example, if you're viewing the video with a resolution of 720p, then the video that's downloaded to your desktop or laptop will match this resolution. This article explains how you can adjust the video quality of a lecture.
If the lecture is not available to download, you can always message the instructor, requesting that they enable downloading. Some instructors are willing to make exceptions, but the final decision is always up to them.
Downloading Courses on The Mobile App
Individual lectures, sections, or entire courses can be downloaded for offline viewing on the Udemy mobile app.