YouTube is full of people who want you to see their material and share it, and yet legally speaking we need to proceed with the utmost caution lest we offend someone’s rights. There is a lot of material available but it is only intended for private use and not for public showings or broadcasting.
The terms and conditions of YouTube mean that the clips are not “pre-approved” for public showing, and the rights of the owner of the clip are not compromised by putting it online.
So – be careful. If you want to use a clip, you still need permission from the owner(s) of the content. You could contact the owner of the clip to obtain permission, but without it the clip should not be shown.