How do I buy a Polygon with MetaMask?

How do I go about purchasing Polygon using MetaMask? Could you guide me through the process step by step? I'm a bit new to this crypto world and would appreciate a clear and concise explanation. Should I first set up a MetaMask wallet? If so, how do I do that? Once my wallet is ready, how do I add Polygon to it? Is there a specific exchange or platform I should use for the purchase? Also, are there any fees or commissions involved in this transaction? And how secure is this method of buying Polygon? Any additional advice or tips you could share would be greatly appreciated.