After Downloading the suggested programs to your pc, I would insist you play with the programs more. Unfortunatly, most of the programs I suggested are supposted to be paid for to use them. Their are other subitutes for them as well but from exprince these work the best. Within using After Effect syou have to get plug-ins, or preset themes, transistions and data. Editing on a computer is the hardest if you're starting out. Computer editing takes a a long time to get into to get in to to my only suggestion is to play with the program and discover new features before you start editing so you can pratice on your transistions and coloring.
Now let me explain how to download videos, there are multiple ways to download videos off youtube into your files set into your computer. I personally use "Savefromnet" but there are other sites as well. If you're tansfering from moblie editing to computer, you should be familair with this site.