You probably already know about YouTube, as it is the largest video sharing site in the world.
It was created in Feb 2005 by some guys who used to work at PayPal. Then a little over a year after, in Nov 2006 it was bought by Google for a lot of money ($1.65B) [source].
On YouTube users can upload, vote and react on other users videos. Some people make compilations of videos into playlist so others can easily find the best videos on a certain topic. It's overall a great source for finding content.
Videos are provided usually in 5 different qualities, depending on the video itself:
The larger the number you choose the better the quality will be, but will also take more room on your computer or device, as well as incur more data transfer (If you're on a data plan). The mp3 option will allow you to download the video in audio format with no video, which is good for podcasts or interviews where you only want to listen.