Parrots learn to speak by mimicking the sounds they hear. People who talk to their parrots will notice that as long as the bird is happy and healthy, it will begin to mimic the sounds it hears, which may be its owner's words.
Birds talk to become part of a flock. They are social creatures that thrive on interaction with other birds and since people are sometimes the only part of the bird's flock, they find a way to communicate with members of the family.
Some parrots learn to speak while other species don't. African grays, Amazon parrots, and budgies learn very quickly. Conures like the green-cheek can only speak a few words and most are only intelligible to their owners.
Young birds will begin to communicate by making a lot of noise to get attention. This is the perfect time for owners to begin talking to their birds. Use phrases such as "good morning" and "good night" often. Never use baby talk with a bird because that is what it will learn. Always praise the bird when it mimics the correct sound.
After a lot of repetition, the bird will begin mimicking the sounds it hears. At first, it may be unintelligible babble, but as time goes on, the words will become more clear. Limit training sessions to no more than 20 minutes at a time, twice a day. A bird that gets bored with its lessons will not learn.