The act of hand feeding makes a baby bird bond to people. The bird then treats the hand feeder like a mother. It is a very rewarding experience to watch baby birds grow and develop. In the past, birds were often taken from the wild and sold into the pet trade. These birds were mistrusting and scared of people. They would bite and scream and did not make good pets. Today, this practice is against the law.
If you have never hand fed a baby bird before, it is best to learn from someone experienced or purchase a baby bird that has weaned, or learned to eat on its own.