Gas fees are charged by the blockchain and are a required expense to keep the blockchain functioning.
Every action on the blockchain is classed as a transaction. Each transaction must be verified to be then added to the blockchain ledger. This takes computer power and miners to take on the job of verification. Payment of gas fee is paid by the user making the transaction.
Gas fees can be adjusted. There is a minimum charge for a transaction and users can opt to pay higher gas fees in order to speed up the transaction. Miners are likely to verify transactions sooner dependent on the fee offered for making the confirmation. This is why some transactions may take quite long to complete. This is often experienced when sending coins and waiting for what feels like forever before seeing the coins reach your wallet. The lower you offer to pay in gas, the longer you wait for verification and completion of a transaction.
Gas fees are paid in the native token currency of the blockchain. For instance, gas fees on the Ethereum blockchain is paid in ETH. Tally Exchange is on the Binance network at present and all transactions are recorded on the Binance blockchain. Gas fees are paid in BNB Smartchain which is the Binance native token.
ETH is a unit of Ethereum. Ethereum is a cryptocurrency. In the same way dollars can be divided into cents. ETH can be divided into gwei.
You see gwei when charged gas fees. This is because gas fees are considerably low compared to the value of 1 ETH, therefore the price is expressed in gwei.
Gwei is also the currency named on the BNB network for paying gas fees. This is not ETH you are spending but BNB. Binance built its blockchain as a clone of the ETH blockchain and did not change the names of certain items. The gwei when operating on the Binance network is representing a smaller denomination of BNB. You are actually paying the BNB gas fee in BNB. The smaller denomination of ETH is gwei. The smaller denomination of BNB is Jager. Therefore, the gas fees in BNB is charged in Jager although it says gwei.