Learn about how one teacher, Mike Christiansen, a 9th grade social studies teacher at Kent-Meridian High School in Kent, WA, uses YouTube in his classroom to transform it into a 21st century learning environment.
Start with perusing these resources to learn about how online video can be utilized with your learners:
Edutopia has a terrific short primer on the options for online video at : http://www.edutopia.org/youtube-educational-videos-classroom
50 Ways to Use Video in the Classroom - including flipping the classroom and having students make video, but focus for this topic on the uses of showing videos: http://community.eflclassroom.com/profiles/blogs/50-ways-to-use-video-in-the-classroom
Seeing is Believing - an article from Education World that may give you some good ideas: http://www.educationworld.com/a_curr/profdev040.shtml
Learn how to search for educational videos on the web using Google Video at
http://www.coolcatteacher.com/how-to-search-google-educational-videos/
(it is really easy!)
Here is a list of sites you can go to in order to finds videos online to show in class:
http://www.watchknowlearn.org/
https://archive.org/details/movies
http://explore.org/live-cams/ - live cam feeds of animals
https://www.truetube.co.uk/search/all?subject=All&topic=All&keystage=All&search=beauty
http://community.eflclassroom.com/video/video/search?q=prediction
https://www.youtube.com/user/teachers
https://www.youtube.com/user/ResearchChannel/
http://video.pbs.org/ or https://www.youtube.com/pbs
http://www.ted.com/ or https://www.youtube.com/ted
https://www.youtube.com/user/khanacademy
Or here is a list of 100 sites if you want to search for even more than I shared here.