I have created a contract, minted some tokens, and I see I have the option to set the Sell and Buy price, but if I do that, Etherscan.io will still show $ 0.00 as the value of my token. How do I actually set Sell and Buy prices? I use 18 decimals
The price being shown by Etherscan is the price of your token on the open market, using data from market sources, such as exchanges. It's not the same thing as the purchase price you set in the contract itself.
Until your token is being actively traded, and people apportion value to it, your dollar price will be zero.