The videos can either be downloaded from torrents or from gossipgirlonline.net, just download the episodes with the scenes you want for your first video first, as each episode take between 30 minutes and one hour to download. You can collect the rest as you go along.
To make your video, you can either practise with Windows Movie Maker or iMovie first (WMM is pre-installed if you have a pc, iMovie if you have a Mac), or go straight in with Sony Vegas. I would recommend going straight for Sony Vegas (which you will have to buy/download), as then you don't have to un-learn what you learned with WMM or iMovie, even though SV is a difficult programme. Most YT users use SV for their videos, as it has more effects and you have much more control over your editing.
I can explain the basics of SV, if you would like me to, but I would recommend watching tutorials on YT as they will be clearer, showing what to do as they explain.
When you gain more confidence, you could consider also getting other programmes such as Adobe After Effects and Particle Illusion and then mix the three programmes to edit your videos. However, I would recommend you wait a little while before trying this :')