To buy and sell cryptocurrency quickly, you need to use a trusted cryptocurrency exchange such as Binance, Coinbase or Kraken. On these exchanges, you can quickly open an account, verify your identity and purchase/sell cryptocurrencies with ease. You can also use a peer-to-peer trading platform such as LocalBitcoins, Paxful or Bisq to find buyers and sellers with more flexible payment methods. Once you have purchased the cryptocurrency, it is recommended that you transfer it to an external wallet for added security.