See the demos on the basic tab or the FAQ:

http://www.tinywebgallery.com/blog/advanced-iframe/advanced-iframe-faq

you can overwrite each setting in the shortcode. src in your case.

Best regards,

Michael

I'm not fully understanding how to make multiple. The FAQs say to add a security key. Where do I find that or how do I create that?

The security key is optional. And you can set one on the basic tab. The first setting!.

Just check the demos: http://www.tinywebgallery.com/blog/advanced-iframe/advanced-iframe-pro-demo

There you have over 50 examples how to set a different src. 

And the faq says to use e.g. 

[[advanced_iframe id="iframe1" src="//www.example.com"]]
[[advanced_iframe id="iframe2" src="//www.example2.com"]]

so very easy to set a different url