Cryptocurrency gas fees are paid when transacting on the Ethereum, BSC, or Polygon networks, in the form of Gwei - a specific denomination of ETH, used for just this purpose. The gas fees that you pay will depend on market activity, network congestion, the speed at which you want your transaction to be completed, as well as a myriad of other circumstances. Traders pay gas fees so that the validators would keep on confirming the transactions happening on the blockchain, and thus, keep the network safe - it can be seen as a type of service fee.