How does Celer work?

Could you please explain in detail how Celer operates? I'm particularly interested in understanding the technical aspects of its architecture and how it achieves the goal of enabling high-speed and low-cost transactions on blockchain networks. Additionally, I'm also curious about how Celer's off-chain technology integrates with on-chain smart contracts and how it manages to ensure security and reliability. Lastly, could you provide some real-world examples of how Celer is being used or could potentially be used in the cryptocurrency and finance industry?