A DEX essentially allows you to swap tokens and create liquidity pools, which means that you don't create (mint) new tokens in general. Only if the DEX has the possibility of staking, then you may create LP tokens (Liquidity Pool tokens) and send them to the stakers in exchange of their standard tokens.
If the contract is verified in etherscan.io, you can call their functions directly without the need of any development. You just need to know the contract address, which functions to call and what values are expected.
On the other hand, you can use libraries such as web3.js or ethers.js to interact with the contract through a frontend or backend.
In Uniswap, most of the functions are available through the Router02 contract. For instance, if you had to create a liquidity pool, then you should call this function (it will create a new pair if it doesn't exist):
) external returns (uint amountA, uint amountB, uint liquidity);
Nevertheless, if you are new in blockchain, it's a bit challenging to start with a DEX. Perhaps you can practise a little bit with simple ERC20 contracts, transfer tokens, iterate through arrays, access mappings, develop code in web3.js to read & write values from contracts, etc and then it will be easier to follow the core functions of DEXes.