The transaction fee on the Ethereum network is called “gas” and is expressed in Gwei (fraction of one ether). This fee must be paid for each transaction or execution of a smart contract. It can be adjusted by the user himself, the higher the gas price, the faster the transaction is executed.
These fees go directly to the miners who process the transactions. Consequently, miners select the transactions with the highest fees first, which can lead to high gas prices when network activity is high. EIP-1559 is designed to solve this and other problems.