When a project wants to list their tokens on uniswap or any other decentralized exchange, then they have to privide their own token and at least one other token (in a lot of cases the second token is a stable coin but it can also be Eth for projects on uniswap, BNB for projects on pancakeswap or other tokens) to that decentralized exchange in order to create a trading pair liquidity pool there. The project owners decide for themself how the ratio between token 1 and 2 and therefore they decide the Initial trading price of their token.