How do I buy BNB on MetaMask?

Excuse me, could you possibly enlighten me on the process of purchasing BNB on MetaMask? I've been hearing a lot about it and am quite interested in adding it to my crypto portfolio. However, I'm a bit clueless about the steps involved. Would you mind guiding me through the necessary procedures? Do I need to connect my MetaMask wallet to a specific exchange first? Or can I directly purchase BNB from within the MetaMask interface? Also, are there any fees associated with this transaction that I should be aware of? I'd really appreciate your help in navigating this process.