First, analyze your website and find out what type of video you will be wnating, and where you wish to put it.
Next, go to Youtube and find the video you would like to be embedded into your website.
Once you have found the video you would like, open it and click the share icon.
After clicking share, choose the embed option. Be sure that the Show player controls and the Show video and player actions options are selected
Copy the iframe element that youtube has provided you.
Paste the iframe element that you have just copied, into your websites code
After pasting the element into your websites code, preview it and see if it has the correct and desired placement and effects.
Here is the video tutorial on how to embed a video into your site.