I'd like to be able to download videos from YouTube, so that I can view them when I'm offline. I can't find any way to do this. Can you help?
You and everyone else. This is such a popular search on the web that you will find tons of CRAPwear installed on your computer if you just click on any item you get when you search for related to download YouTube videos. So don't do that.
DO NOT OPEN A WEB BROWSER AND SEARCH FOR DOWNLOAD YOUTUBE VIDEO or you will be sorry.
The article below shows you how to legitimately download YouTude videos.
Actually they are not legitimate either. It is illegal to download videos from YouTube unless the author makes that possible. On the other hand everyone needs to do this occasionally and you'll find several different ways to do this.
Personally I found an add-in for FireFox that make it safe and easy to download videos from YouTube for those few times I need to download a legal copy of a video online.
In any case I can't repeat enough do not search online for download youtube videos or you will be bitten by bad malware. It's just too easy a target.