It is easier than you think, especially if you are used to listen music on YouTube. There are a lot of easy to use websites, where you need just to insert the link to your video and push the button "download". I am sure that it is much more useful. I have been already used this option for 2 years to download lectures and podcasts for my university. I recommend you to try https://youtubemp3.la, because there is possible to install the app on your phone. Of course, it is totally for free. Hope that I have helped you.