©HEAT-O-SHEET

You can add and embed pictures as following:

<img src="this is the source of the pic" alt="this is a description of the pic if it won't load" / >

Please note that this is a self closing tag. Height and width can be styled either inside of the element or via CSS.
Always add an "alternative description" for accessibility reasons or a "title" for a mouseover description.

The result:

You can add and embed videos as following:

<video controls width"xxx">
<source src"the source of your video" / >
Then you can add some information about the video if it's not being played by the browser for accessibility reasons.
< /video>

The result:

You can add and embed audio as following:

<audio controls>
<source src"the source of your audio" type="type of audio"/ >
Then you can add some information about the audio if it's not being played by the browser for accessibility reasons.
< /audio>

Note that you can add a caption with the <figure> element to make the audio more descriptive.

The result:

An old and more and more obsolete way of embedding different kinds of media is by using the <embed> element.
MDN says and I cite: "Keep in mind that most modern browsers have deprecated and removed support for browser plug-ins, so relying upon <embed> is generally not wise if you want your site to be operable on the average user's browser."
If you want to use it nevertheless, you can do as following:

<embed
type="type of media"
src="source of media"
title="descriptive title for accessibility"
width="xxx"
/ >

The result: