I have not used terminal before. I got the following instructions:

Just follow these three easy steps to download your first video.

- 1. Download youtube-install
script<www.nuxified.org/.../youtube-install.sh>
- 2. Run the youtube-install script in the terminal as root (e.g. sudo
./youtube-install.sh)
- 3. If the script says "youtube installed" you can start downloading
YouTube videos like this: youtube-dl URL, where "URL" is your YouTube
video URL.

I download the install script it is in the download folder. What is root?
how do I run this program in terminal?