Please help! what is the diamond hands exercise and how is it performed?

As in push up: If referring to push-ups, this is a form of close grip push up which shifts the stress of a push up to accentuate triceps contribution. In essence you assume a "standard" push up position but instead of your hands at approximately shoulders with, you bring your hands so that they are touch at the forefinger(2nd) and thumb, forming the "diamond". You then rise and lower as you would normally.