What chamber receives blood from the right atrium?
Deoxygenated blood from the body will enter the heart's right atrium. The atria (left and right) will contract and send blood into the ventricles. Then, blood that is in the right atrium will move into the right ventricle. As it moves from the atrium to the ventricle, the blood will pass through the tricuspid valve. This valve helps ensure that blood does not flow the wrong direction through the heart. From the right ventricle, the blood will then be pumped out of the heart to the lungs. The blood will drop off the carbon dioxide that it is carrying, and it will pick up oxygen. Once the blood is oxygenated, the blood returns to the heart and enters the left atrium. The left atrium will contract and send blood to the left ventricle. The left ventricle will then contract, and oxygenated blood is sent out to the body. It will return to the right atrium after exchanging its load of oxygen for carbon dioxide. In short, blood goes from the right atrium, to the right ventricle, to the lungs, to the left atrium, to the left ventricle, to the body, and then back to the right atrium to start over.
Short answer: the right ventricle.
Long answer: Using the right atrium as an anchored starting point, the right ventricle is where blood would flow to next in a normal human heart (in all normal mammalian hearts, for that matter). It can be difficult to think about the direction of blood flow through the human cardiovascular system in a linear sense because in reality it's an ever-continuous cycle, but here is a quick-and-dirty flow chart to remember the order of blood flow, using your chosen right atrium as our starting point:
Right Atrium -> Right Ventricle -> Pulmonary Artery -> Pulmonary capillaries -> Pulmonary Vein -> Left Atrium -> Left Ventricle -> Aorta -> Arteries and arterioles -> Systemic capillaries -> Venules and veins -> Superior and Inferior Vena Cava -> and back to the right atrium.
Consulting online videos may help with comprehending this complex system more deeply.