Watching videos on YouTube couldn't be easier—just come to the site and browse around, or search for subjects that interest you. To save your favorites for later, you need to sign up as a member, and then click the 'Add to Favorites' link underneath the videos you want to watch later. You can also create playlists to group favorite videos together into your own personal categories.
Tags are keywords that describe videos. For example, a surfing video might be tagged with "surfing," "water," and "waves." Users who enjoy watching surfing videos can then search for any of those terms and that video will show up in their search results. Tags help you find new videos you might like to watch, and also help you label videos you upload so that other people can find them more easily. The larger the tag appears in the list, the more videos use that tag.
To remove one of your videos, simply log in, go to http://www.youtube.com/my_videos and click on the 'Remove Video' button next to the video you'd like to remove. You are only able to remove videos that you have uploaded.
YouTube doesn't save your searches, but your browser probably does. If you don't want to see your previous search terms displayed in the search field, you need to clear the search history in your browser.