How can I buy or sell cryptocurrencies with fiat money?

You could use a service like eToro. The service of eToro is integrated in Coinranking, so with only one click you are directed immediately to where you can buy bitcoin, ether or litecoin.

You could also use a service like Coinbase to buy cryptocurrencies with dollars, euros or other fiat currencies. If you follow this link you even get $10 worth of cryptocurrency for free: https://www.coinbase.com/join/5a0b0ab35e18250227c7c45a.

After you've bought Bitcoin or Ethereum for example, you can exchange them for another cryptocurrency on Binance: https://www.binance.com/?ref=35424440.