How can I buy BNB on MetaMask?

Could you please explain to me the steps I need to follow in order to purchase BNB on MetaMask? I'm new to this and want to ensure that I'm doing it correctly. Do I need to have a specific type of account or wallet set up? And what about fees, are there any associated costs I should be aware of? Additionally, is there a minimum amount of BNB I can purchase, or can I buy any quantity I choose? Also, how long does the process usually take? Lastly, is there any security measures I should take to protect my investment? Thank you for your help in guiding me through this process.