How to buy and sell Polkadot?

Could you please elaborate on the process of purchasing and selling Polkadot? I'm interested in understanding the steps involved in acquiring this cryptocurrency, as well as the methods to sell it securely. Could you provide insights into choosing a reliable exchange platform for these transactions? Additionally, would you mind sharing any best practices or safety measures to consider while engaging in Polkadot trading? Thank you for your assistance in clarifying this process.