There are two main differences. The first is the meat used - beef for burgers (like these grilled hamburgers) and pork or chicken for sausages. Although, as you can see here, sausage CAN be made with ground beef. The second main difference is the seasoning. A burger is often seasoned very minimally, with just salt and pepper. Sausages are heavily seasoned and often contain spices such as paprika, sage, and thyme.