In fact a lot of due to their state or lack of educating or physical appearance thinks they cannot be useful to God, but they forget that the bible says God looks at the heart if man.
Moses felt God couldn't use him to deliver the Israelites from the Egyptians, because he was a stammerer, but look at what Moses achieved.
If you feel you ate useless, just try God, you are not, God does not think like a man, he can use you and likewise me.