Yes, you can download any of the lessons and save them to your computer, iPhone, iPad, tablet, or other device, to view when you are not connected to the Internet.
After you order, please go to this page:
The full download size is approximately 3.5 GB, but again, you can download only the specific lessons you'd like.
You can of course still log in to watch all of the videos online anytime, or download them again, if needed.
Once you download the videos, you'll need to sync the video files you want to watch onto your device using the iTunes software.
Depending upon your operating system, you should be able to save the videos to a folder of your choice and play them in Gallery or with the built-in video player. If the built-in player can't play them, you'll need an app that can. Google Play has a lot of those. My personal favorite is MX Player. Other good ones are VPlayer and Mobo Player. And there are numerous others. These will play just about any video format. The formats it can't play are rare.