You can upload videos from YouTube, Vimeo, WeVideo, Flipgrid or from your own computer provided they are in the MP4 format (here is a link to a free online converting tool).

Create a video item and simply copy and paste the URL link and it will automatically upload. Below is the creation tool walkthrough but you can skip to the specific segments on the links below or through the comments on the video on YouTube.

Upload from YouTube

You can also upload a specific segment of a YouTube video. Find out how here.