If you need help with graphic design, you can find it on the online design portals. Usually on such sites there are many instructions, tips, recommendations, explanations, but the most important thing is that  you can find free samples made by professionals, for example, here https://www.ls.graphics/free-mockups/business-card-mockup are examples of cover layouts for different types of books. You can use them to create your designs. Very convenient, isn't it?