Okay, rather simple - you get the website address but it must in the file extension - .jpg, .gif - ect. Site usually doesn't matter but some sites don't do third party hosting. 

Then just place it between the [code][img][/img][/code] and it should pop up.

If you are worried about sites, save the file to your hard drive and upload it to your profile page under the image tab. Then you can link it directly from this site and not have to worry about what site it is on or anything. 

For example...
[url=https://images.hellogiggles.com/uploads/2016/04/14013812/giphy28.gif]https://images.hellogiggles.com/uploads/2016/04/14013812/giphy28.gif[/url] placed between the [code][img][/img][/code]

pops up as this...

[img]https://images.hellogiggles.com/uploads/2016/04/14013812/giphy28.gif[/img]