How to make Instagram video/photo edits?

I have a fan account and I see all these awesome Photoshop edits, memes like this: https://instagram.com/...n-by=sokka
and music video edits. I've asked some accounts how to but no one answers. What computer or iphone apps are good for making these pictures and videos?

First, you rip an image (that is likely not licensed as creative commons) off from the internet. The next step is to use a graphic editor (such as the open source GIMP or Paint.net) to add text (sometimes something funny and other times something stupid or boring such as in the provided sample).

That is pretty much all they did. I don't know about any open source video editors, but I'm sure that you can find some by searching in Google for them.