In order to add video to your website, the first step is to upload your video to a video streaming platform such as YouTube or Vimeo. Once you've done that, it's easy to embed the video into any page of your website.
The admin text editors make it very easy to embed videos on your pages, in any text area. Just click the Video button in the toolbar, and there you will paste the YouTube or Vimeo video page address* into that box.
* Note that you need to paste just the video page address - NOT the "embed code" for the video. So when you're on your video's page on YouTube or Vimeo, copy the page's URL address from your browser's address bar, and that's what you'll paste into the admin.
You can also embed videos from other video streaming platforms besides YouTube and Vimeo, although the process is slightly different. In this case, you would copy the entire "embed" script code that they provide for the video, then in the admin text area click the "Embed Code" button at the right side of the toolbar, then paste the embed code into the popup box there.