One of the methods used by exchanges to listing new coins to start trading on their exchange is through voting from the community and usually there will be rewards that will be obtained by voters and the rules for voters are that they must have these coins to be eligible as voters, dunno for now if its still in use.

Each exchange has its own rules but usually there will be a fee that must be paid by the developer as a condition of listing, Binance said they do not collect fees from coins that want to be listed there but go through checks whether the project is feasible enough to be included. All one has to do is make contact with the exchange and there's usually document to be included but that's when dealing with a major exchange small exchanges have a way that might be easier.