Gas is the unit that measures the amount of computational power required to perform a transaction on the blockchain. Akin to the gas you put in your car, this gas fuels all specific actions that you execute on the blockchain.
For every transaction on the Ethereum blockchain, you have to perform a series of computational steps. Gas fees do not have anything to do with liquid fuel consumption or the impact of mining on the environment. Rather, it is the reward given to miners for putting transactions in the blockchain or executing them.