How To Do A Mockup. Like i mentioned before you will often find a jpg preview a psd source. Start with an image for your mockup design.
You can draw it or use a photo. These days the best way is to select a digital web mockup tool that enables you to create everything with simple clicks or by dragging and dropping components. Open and locate the smart object.
You will find plenty of psd mockup files to work with around the web this includes both.
Like i mentioned before you will often find a jpg preview a psd source. Convert that shape to a smart object. You might also want to adjust. Adjust the perspective to match the rest of the scene.