How to get the quantity supply?

Could you please elaborate on the process of determining the quantity supply in the context of cryptocurrency? Is it a fixed number set by the creators, or does it fluctuate based on certain factors? How does the market demand and adoption rate impact the quantity supply? Are there any mechanisms in place to adjust the supply in response to changes in the market? Understanding the dynamics of quantity supply is crucial for investors and traders alike, so I'd appreciate a detailed explanation of the process.