If toi have a PC toi should have windows movie maker and if toi have mac it should have imovie.
Find whichever one on your computer and open it.
There are different ways to get vids/vid clips but I only know how to get them from youtube.
I use YTD Video Downloader (find it online and download to your computer). Go to Youtube and copy the link then paste it in the downloader. Once it downloads click on the folder and make sure the video is in your downloads folder.
On the movie maker click "Add vidéos and Photos" Go to your downloads and find the video toi got on Youtube and mettre en ligne it to the maker. Once toi have at least one video uploaded click on "add music". I use musique from my itunes but I think other things can be used. Find the song toi want and click on it to use for the video. Under projects drag the audio mix all the way to the musique symbol to annuler out the sound from the Youtube vid. toi can cut and supprimer and rearrange video clips to make the video toi want. There's plus to it but that should get toi started. Hope it helps :)