Question

How is 90 degrees north latitude different from from 90 degrees south latitude

Answer 1

They would be on completely different sides of the earth.

The north one would be in the northern hemisphere, and 90 degrees latitude south would be in the southern hemisphere.

Respectively, the north pole and the south pole.

Answer 2

Difference is direction:

90 degrees north latitude---is the North Pole---the furthest point North of the equator.

90 degrees south latitude--is the South Pole--the furthest point South of the equator.