Maybe every youtube user is just an idiot, but we've been unable to figure out this part so far.  Maybe we need some documentation or training to use the system in the way the developers think it should be used.

The high-level purpose of this site is to load/share/watch videos.  We subscribe to video producers so we see when there's something new.  Once we've watched a new video, if we like it, there are various things we can do to make sure we can find it again if we want to watch it again.  There are actually very few videos that I choose to bookmark in any of the available ways.

For all of the rest of the videos, the one's we've watched and never want to see again (ie a political report pertinent to today), or those that simply don't appeal to us, what method do the site designers suggest we use to determine which videos we've already watched, and which one's we've decided not to watch?  I assume they must have a process in mind.  There must be some method they personally use or a function they have designed into the application which will allow users to not have to memorize which of the hundreds of videos listed in the enormously tall stack of icons, we've already watched.

Please, point us to the End-User Training Manual.  We're willing to learn.