A mockup is a visual way of representing a product. While a wireframe mostly represents a product’s structure, a mockup shows how the product is going to look like. But still, a mockup is not clickable (just like the wireframe). As opposed to a wireframe, a mockup is either a mid or high-fidelity display of design.
A mockup helps you make final decisions regarding a product’s color schemes, visual style, typography. With a mockup, you can allow yourself to experiment with the visual side of the product to see what looks the best. Here again, you can ask your potential users for feedback and make the necessary changes right away. This will save you way more time than getting back and making adjustments to the UI after you have launched the product.s opposed to a wireframe, you cannot sketch the mockup. You might need to use a mockup tool. There are plenty of them, too. You might want to try Marvel, InVision, or Moqups.