Something that's below is underneath. If your kite is flying below your brother's, it means his kite is above, or higher than, yours.
Anything that lies lower than some other object is below it — a basement is below the first floor of a house, and the ocean floor is below the water's surface. Below can also describe something that ranks lower: "My dad said if I get below a 90 on the math test, I can't go out this weekend." The word below was rarely used until the 16th century — most experts credit Shakespeare with making it a popular alternative to "beneath."