I have been meaning to do this since I started selling mockups on Etsy, Creative Market and The Hungry Jpeg websites, and finally I have created 2 videos for you to watch. One explains how to put a design onto a mockup image using Picmonkey, a free online editing tool and the other explains how to overlay images using Photoshop CC.
These are the first video tutorials I have done, so I apologise for any mistakes:)
These videos are useful if your designs are jpegs and have a white background that you want to eliminate from your design when you overlay them on top of the mockup image. If you have a png file the chances are this will have a transparent background so the white box/rectangle round your design will not be there. If you have any questions please don’t hesitate to get in touch
Using Photoshop CC