Blockchains are decentralized networks: not operated by one particular company or individual but by multiple anonymous agents. 'Gas' is the compensation paid to miners and stakers, the agents who help make transactions possible in a blockchain network. Originally used in the Ethereum network, the term 'Gas' is now commonly used to refer to similar fees on other blockchains.
An easy way to think of 'Gas' is like it’s fuel for your car: the farther the destination (the more demanding the process is on the network) the more fuel you will need (the more gas you must pay for the process to be completed).
Gas fees change all the time
Nearly all transactions cost gas, but since some operations require more work than others miners and stakers need to be incentivized accordingly to complete the more demanding tasks. Thus, gas fees vary over time depending on the type and the number of transactions queued on the blockchain at a given moment - it is normal to pay a different gas fee to complete the same transaction in two different days or even at different times on the same day. When the volume of transactions is high, urgent and/or more complex operations cost a higher gas fee.
Gas fees are always paid in the native coin of the network that the transaction is taking place on: ETH for Ethereum, MATIC for Polygon, AVAX for Avalanche, etc. Don't have the specific coin you need? You may choose to swap some of the other coins you own, or buy from an exchange.
Finding out the gas fee for a transaction
Most crypto wallets will show the gas fee cost of a given transaction before you confirm its execution. Zelus wallet certainly does so for all transactions - and we also added a brief explanation of what gas fees are for those who are not familiar with the term.
Why there are no gas fees in centralized exchanges, like Binance or Coinbase
Many centralized exchanges operate similarly to a bank: since they have full custody of your funds they do 'off-chain' bookkeeping instead of actually transferring crypto to or from your blockchain address. In simple terms: crypto doesn't actually move, thus gas fee is not required. Users pay instead a 'trading fee' to the exchange every time they do a transaction, as well as a 'withdrawal fee' when they actually move any funds from the exchange into their own crypto wallet.