Need explanation about ranking/SEO
 

Hey there guys,
So I ve just started tube site, like 2 months ago. In that period I was uploading as much videos as I could. So now I am curious. I have SEO plan that is done. I have keywords that I ve implemented mostly thru tags, but not descriptions or titles of the vids. So I wanna know, I can't rank thru tags only? I need titles and descriptions to be done so google could rate my site and vids, so it could rank me up?