How are cryptocurrencies born?

Could you elaborate on the process of how cryptocurrencies come into existence? I'm curious to understand the genesis and birth of these digital assets. Do they arise from a central authority or is it a decentralized process? How do their creation differ from traditional currencies? Are there specific algorithms or protocols involved? Could you provide a high-level overview of the steps involved in the birth of a cryptocurrency? I'm particularly interested in how the supply of these currencies is determined and how their value is initially established.