I just don’t know how the theme authors are able to come up with pictures like example http://1.s3.envato.com/files/71497592/preview%20images/01_Image-Preview.__large_preview.png
if you guy know how they do it plz comment down.Do they use an online site or is it the wonders of photoshop??
Like charlie4282 said, just search on graphicriver for “responsive mockup”.
You’ll find a couple of items very easy to use, you’ll just have to replace in the item, in Photoshop, in the smart layers, the screen mockup with yours.
I am not so good in Photoshop but it took me less than 3 minutes to create something like that with a template bought from graphicriver