This question has been coming up on the forum a lot lately, so I'll post the answer here. "I just got a Quaker and it keeps biting me! Why is it doing this and how can I make it stop??"
Stop trying to handle it, your bird is telling you "No, I don't like this.".
The key word here is "just". If you just got a Quaker, no matter what age it is, you need to give it time to adjust to its new environment before you try to handle it too much. Quakers have the intelligence of a 3-4 year old human child, so just imagine what a toddler would do if it was suddlenly torn away from everything it knew and put with strangers who kept trying to handle it. You have to give it time. How much time depends on the bird. It could take a week, or it could take six months to a year, if the bird is older or has trust issues. Like people, some birds are cuddly and some are more distant.
Wait three days before you try to touch it at all. In those three days change the food, water and papers (or whatever is in the bottom of the cage), spend lots of time talking to your bird, sit next to the cage and read books aloud, sing if you want. Get your bird used to your voice.
You can also play games with your bird. Human babies generally love games where you look at them and as soon as eye contact is made, you turn your head away quickly. Parrots love that game too. A variation of that game is blinking. You make eye contact with your bird and blink. If he's comfortable, he'll blink back at you. My Cockatiel's favorite game is the tapping game. He'll tap on something (his cage bars, a perch, the coffee table, the wall...once he even tapped my head when he was up there! - anything that makes noise (well, my head didn't really make noise but I could feel it, LOL) - with his beak and I tap back to him.
Then you can start giving healthy treats through the cage bars. Some healthy treats would be peanuts or sunflower seeds (not too many of these, because they're high in fat), plain popcorn (no salt or butter), pieces of fresh fruit (dried is good too, as long as it doesn't have added sugar), small amounts of whole wheat bread (I just learned that toasted is better for them), and veggies.
Once your bird will take treats from you and eat them (not just drop or throw them), you can open the cage and LET THE BIRD COME OUT ON ITS OWN. This is extremely important. Don't reach in and try to get the bird out on your hand yet. If the bird wants to come out, it will. If it wants to come hang out on you, it will. If it bites, don't yell or say "Ouch" or anything, parrots are drama kings and queens. If you react loudly the bird will most likely bite again to get the same reaction. Calmly put the bird back on or in the cage.
I hope this helps. If anyone wants to add anything, please do!