Supplementary angles are two angles that add up to 180 degrees. They can be adjacent or non-adjacent, meaning they can share a common arm and vertex or not. When two supplementary angles are adjacent, they form a straight line. Complementary angles, on the other hand, are two angles that add up to 90 degrees. To remember the difference between the two, you can use the starting letters of the words themselves. "C" stands for corner, which reminds you of a right angle, which is 90 degrees, so complementary angles add up to 90 degrees. "S" stands for straight, which reminds you of a straight angle, which is 180 degrees, so supplementary angles add up to 180 degrees.