This is a great postcard mockup with a nature-friendly theme. The styling is simple, A person holding a card in the air shows a kind of excitement in the picture, And the peaceful natural environment in the background suit it very well.
You are not going to have a hard time working with this mockup. Choose your best design, and then go to the smart layer and double click on that. Then you can insert your design into the mockup and see your artwork in real life.