How to buy smog with MetaMask?

Excuse me, I'm a bit confused about the process of purchasing smog using MetaMask. Could you please clarify the steps involved? Do I need to have a specific amount of Ethereum in my wallet beforehand? Also, is there a specific marketplace or platform that I should be using to make this purchase? Additionally, are there any fees associated with buying smog using MetaMask, and if so, how are they calculated? I would really appreciate it if you could provide a detailed and step-by-step guide to help me understand the entire process.