You will need to download the videos which you want to watch offline.
To do this, click the ellipses (...) on the right of the video name and then click on "Download Video". Download is possible for most videos, except for some Level I videos which are hosted on YouTube.
For more help with downloading, visit this help page: https://ift.freshdesk.com/support/solutions/articles/13000069568-how-do-i-download-videos-to-watch-later-when-i-am-offline
When you are offline you don't have to do anything special.
Just don't log-out of the app and then when you go offline just start the app and browse to the videos which you downloaded.
If you had downloaded that video, then it will play.
If you had not downloaded the video, you will be told that you need to go online to watch it.
1) To login - you do need to be online. So if you plan to use the app when offline, then don't log-out of the app!
2) The downloaded videos are hidden and encrypted. So this means you can watch them only from within the IFT App.