Gas is the amount of computational work you will have to pay in order for your content to be included on the Ethereum blockchain. You will have to pay the gas in Ether (ETH, although gas is priced in Gwei, which are 1 billionth of 1 ETH), which you can purchase via MetaMask and a cryptocurrency exchange such as Coinbase. Gas costs are paid to the miners carrying out that computing effort, and are variable based on traffic on the Ethereum network, sometimes changing within the span of a few minutes. You can familiarize yourself
MetaMask will select and show you a sensible gas price by default, and you can customize it by clicking the “Edit” button above the gas price.
When sending a transaction, your wallet will automatically set the appropriate gas limit, which is separate from the gas price and should not need adjustment.