Quantum computers perform calculations using quantum mechanics and qubits that can represent superpositions of states. While classical computers use bits that are either 0 or 1, qubits can be both 0 and 1 simultaneously. This allows quantum computers to massively parallelize computations. Some potential applications include simulating molecular interactions for drug development, breaking encryption standards, and optimizing machine learning models. Several companies are working to develop quantum computers, but building large-scale, reliable versions remains a challenge due to the difficulty of controlling qubits.