Use the <video> tag to add video to your website. Create a video using Screencastify. Make sure to provide multiple sources for you video (file types) to accomodate various browsers. You may need to use a conversion tool to create the required file types such as .ogv, .webm, and .mp4.
Notice the parameters (attributes) such as controls, width, and height. These parameters change the way the video player functions.
Here's an example of the code you will need and the parameters for your video player.
<video controls="controls" width="480" height="360">
<source src="screencast.ogv" type='video/ogg>
<source src="screencast.webm" type='video/webm' >
<source src="screencast.mp4" type='video/mp4'>
<!-- Notice for non-supporting browsers -->
Video is not visible, most likely your browser does not support HTML5 video
</video>
You can also add the poster attribute to provide an image of your video
Here's a little help: W3CSchools