firs you have to find the video you want to download (SEARCH VIDS in the menu)
Once you've found the video, you can go to this video's description page. At the bottom of this description page are the download links.
then it depends on the video you're trying to download... there are several types of links :
LOCAL : left click on LOCAL and wait...the download should start
DIRECT : right click on DIRECT and "save link as"
INDIRECT : left click on INDIRECT , you'll be redireced to the creator's site where the download instructions are explained
no link : the video can't be downloaded
was it of some help ?