How to buy BNB smart chain on Binance?

Excuse me, could you please explain the process of purchasing BNB Smart Chain on the Binance platform? I'm a bit new to this and would appreciate a step-by-step guide. Specifically, I'm interested in knowing how to navigate the Binance interface, select the right BNB Smart Chain option, and complete the transaction securely. Additionally, are there any fees associated with the purchase, and how can I ensure that I'm getting the best possible exchange rate? Thank you in advance for your help.