I'd be happy to help. Unfortunately you cannot insert them directly into Mediashout 5. There are copyright regulations that prevent us from facilitating this. However, you can save the Youtube video or download it as a video file to your computer itself, then just go to Insert > Video and point to the file like you would bring in any other video. For this you'd need an application to download and save the Youtube videos. There are free and paid options out there and we recommend being careful in choosing one because some can have spyware/viruses. For that reason you may go with a paid one to be safe. Of course we do recommend clearing any permissions you need with the copyright holder for whatever video before using it.
Let me know if we can be of more help!