If you have a video file that you would like to add to Tettra (under 50mb), you may add it to a page like any other file. Drag the file onto the page, and wait for it to upload. It should look something like this:
Once the video is uploaded and the page is saved, any team mate will be able to access the video by clicking on the video name in the tettra page.
Alternatively you may want to embed an existing video that is on a video service like youtube or vimeo: http://support.tettra.co/editor/how-to-embed-videos-and-rich-web-content