How does USDD work?

Could you please elaborate on the mechanisms behind the operation of USDD? I'm particularly interested in understanding how it maintains its stability and how transactions are processed within this cryptocurrency. Also, could you explain the role of collateral and how it contributes to the overall functionality of USDD? Furthermore, what are the potential risks associated with investing in this type of cryptocurrency, and how does it compare to other stablecoins in the market? I'm keen to get a comprehensive understanding of how USDD works and its place in the cryptocurrency ecosystem.