Step 1

Find a video you would like to use like this one I found below. Then use the correct code you need, and another way is to find the video on youtube and it will give you the full correct code.

video source

Video from computer

video source

Video from Youtube

Part 2

Make sure your code is right, but the easyiest way is to use youtube.

video source

Link the code, put it as "video/mp4".

video source

Pasted youtube embed, and enjoy the video you have embeded.

Example
" frameborder="0" allowfullscreen="">