I couldn't understand any popular science books and articles about quantum mechanisms. And that's why I post here to find an answer to my years-long confusion.

Popular science articles tell us that a qubit could represent both 1 and 0 at a time. So, it raised a question in my mind: how could the QPU perform a calculation?

For example, if I need to calculate 1+0=?, there should be a qubit1=1 and a qubit2=0, and then, qubit3 to store the result of the calculation. However, as the articles told us, qubit1 and qubit2 may be both 1 and 0 separately. So, eventually, will the result of the calculation be 0, 1, or 2? How could the computer determine the value of an uncertain qubit?