Too Long; Didn't Read
According to Wikipedia, quantum computers are devices that harness the collective properties of quantum states, such as superposition, interference, and entanglement, to perform calculations.
To fully understand quantum computers you must understand quantum physics(at least a watered-down version of it 😅). I tried to use as many simple words as possible, but If at any point in time during my explanations you don't understand anything remember this quote by Richard Feynman, the father of quantum computers - "If anyone tells you they understand quantum mechanics then they don't understand quantum mechanics".
In essence, no one understands quantum physics, even the pioneers.
Quantum physics is physics that deals with the behaviour and interaction of particles (i.e protons, electrons etc) in the quantum realm and how they affect our physical world.
Now when the concepts of quantum physics are used to manipulate particles to perform computation, quantum computation comes about and this then brings about quantum computers.
In simple words, quantum computers are computers that make use of quantum physics concepts to process data and output it as information the same way normal computers work but with atomic particles.