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Cryptocurrency exchanges allow you to trade cryptocurrencies freely, but don't expect to buy and sell all your tokens everywhere and to do so anonymously. In reliable platforms, you will need to be thoroughly verified before you start trading, but there are also exchange offices with less formal requirements. Keeping (HODL) the purchased currencies on the stock exchange is not advisable, it is better to do it in wallets, i.e. special applications. Exchanges are generally well secured, but have fallen down from time to time. Pay attention to the commission of the platform and the fact that they usually have their "favorite" tokens that they promote.