Use the Law of Detachment to draw a conclusion.

Question

If the measures of two angles have a sum of 90 degrees, then the angles are complementary.
measure of angle A + measure of angle B = 90.

Could someone help explain the Law of Detachment so I can understand it better? And also, how exactly would I take a conclusion from that and phrase it? (Would it be an if/then statement?)

Thanks in advance. :)