How to download YouTube videos onto un-jailbroken iPhone 4S?

Hi, I have an iPhone 4S which I have not jailbroken… Yet. I'm wanting to download a video from YouTube that is about 3 hours long onto it so that I won't have any loading problems while watching it on the road. I've installed a downloader app which SAYS you can download videos but I can't get it to work or at least I don't know HOW to get it to work… It seems like it just copies the link and opens the video but it doesn't actually download onto the phone. I would like to watch it as if I was watching any other movie that is under the "Videos" app… Is there any step-by-step way that I can learn how to do this. I'm not really technologically smart as to what I need to do, so a picture tutorial will be the best thing for me…

First go to the video then copy its link then go to

http://en.savefrom.net/

when the website opens.enter the video link in the search box then press download and finally choose the video format to download it.

ImTOO iPhone Transfer Platinum is an online video downloader and converter which can download and convert online videos from top online video websites.such as YouTube, Metacafe, Dailymotion, Break, Vimeo, Revver, Blip, Vidilife and Stickam.