Every transaction on the Ethereum blockchain is required to cover the computation cost; this is done by paying gas to the transaction originator. Each of the operations performed by the transaction has some amount of gas associated with it. 

The amount of gas required for each transaction is directly dependent on the number of operations to be performed—basically, to cover the entire computation.

In simple terms, gas is required to pay for every transaction performed on the Ethereum blockchain. The minimum price of gas is 1 Wei (smallest unit of ether), but this increases or decreases based on various factors. The following is a graph that shows the fluctuation in the price of Ethereum gas: