Before a new currency exists, it doesn't exist. Someone has to mint it. It has to be inflated into existence, in the monetary sense. How is this done?

For a state or central bank the answer is obvious: The state or bank itself prints it.

For a private actor the technical means is perhaps less obvious, but the actor behind the currency obviously gets to decide.

For a decentralized open source project, it is less clear. You could do it so every node in the system gets a piece of every newly printed unit of currency, but if it is free to run a node everyone could just run a billion nodes and take all the currency for themselves.

Bitcoin solved the problem with Proof of Work, which is elegant because both the double spend problem and the minting problem is solved together. Every node has to prove it has run a unit of useless computation and inflation is spread evenly across worker nodes. This led to a split between nodes and miners with the use of specialized hardware, but the basic premise still holds.

Crypocurrencies in general are very different. Ethereum, the second most popular, was created by a private actor and the that actor decided to print 72 M for themselves and promptly sold 80+% before the release of the software which gave rise to the term ICO which was very trendy for several years. After the initial release inflation continued according to the miner model.