Gas is a unit of computational work to perform transactions or smart contracts on the blockchain. It is not a coin, not some part of a token, it is a dynamic metric through which it will be billed already in chosen blockchain. It is used in calculating the cost of a transaction. The amount of gas for a transaction depends on its complexity.
It is important to understand that different types of transactions require different amounts of gas. Just like with electricity or gasoline: a powerful appliance or engine will spend more compared to a weak one.
For example, that's how gas fee message looks like in Ever Wallet