How do I buy coins with MetaMask?

Excuse me, could you please elaborate on the process of purchasing coins using MetaMask? I'm a bit confused about the steps involved and would greatly appreciate it if you could guide me through the entire procedure, step by step. Are there any prerequisites or specific requirements that I need to fulfill before I can start using MetaMask for coin purchases? Additionally, is there a way to ensure that my transactions are secure and that my funds are protected from potential risks? Thank you in advance for your assistance.