Quick/automatic approach:
Enable the module "Islandora Video Embed", and in the Blocks menu (Structure -> Blocks), add the Video Embed Code block to a page region such as Sidebar Second.
Now, when you view a Video object, a block appears containing embed code you can copy and use on any website.
Manual approach:
Get the full download link from your object's Manage page, and include the video's complete filename.
For example: to embed https://arcabc.ca/islandora/object/kora%3A296
Example embed code:
<video width="320" height="240" controls>
<source src="https://arcabc.ca/islandora/object/kora%3A296/datastream/MP4/download/fi..." type="video/mp4">
Your browser does not support the video tag.
</video>
Result: