Here, I made a slideshow in JSFiddle and then embedded the fiddle here using an iframe. (Click on result to see the slideshow.)
To make the iframe, use this format:
<iframe src="URL OR OTHER SOURCE CODE" width="100%" height="300" style="border:none;"> </iframe>
The information in red is adjustable for your specific height and width.
Note: Many of the programs you use will create the embed code or you, and some will use script instead of an iframe. Or they may offer a choice.
For instance, here is an iframe from a multimedia graphic I created using Flourish. Flourish allows you to generate either iframe or script code. Which to use depends on how and where you might use it, but it’s easier to adjust the width and height with an iframe.