What we all have been saying applies to your ear, not the keyboard. So, if you learn a song or a scale and know what key it is in, then by listening to a few notes you should be able to tell how far up or down your reference scale it is. Let's say you play Misty in Eb and someone comes up and starts singing it - in a different key - as you hear the first three notes ask your self "is it higher or lower than mine." Then by using your reference scale, determine if it's one or two or two and a half steps aay from you. As was said earlier, you have to know basic major and minor scales to do this. Now, does this help?