All tokens are listed on DEX Screener automatically as soon as they are added to a liquidity pool and have at least one transaction. You can use the search bar to search for any particular token by its name, symbol or address, as well as a pair address.
DEX Screener automatically looks for token information from external token lists, such as CoinGecko's. Once a token is present on such a list, all of its information will be displayed on DS automatically.
DEX Screener uses the following formula to calculate fully diluted valuation for any given token:
FDV = (total supply - burned supply) * price
In most cases, FDV will be the same as market cap, but there can be exceptions. For tokens that don't burn supply that isn't in circulation, DS will look for self-reported circulating supply from CoinGecko, and automatically use that amount to calculate market cap instead.