Before we use it, let's know what is gas(limit) and gas price.
What does gas and gas price mean?
To do anything on the Ethereum platform, you need to pay for it, and the payment (or fee) is calculated in Ether (ETH) via an intermediary benchmark called gas limit and gas price.
Usually, when someone is talking about “gas” in Ethereum, they are referring to “gas limit”. This simply means some amount of fuel is required to execute that operation or run that particular smart contract code.
Gas is a unit that gets translated further into Ether (ETH) as a cost of performing that action or work. The requester pays this cost to the blockchain miners who mine and validates that transaction or action on the blockchain network.
If you want to pay less for your transaction, you can do so by varying the gas price which also determines the final cost (or Tx fee) of the transaction. On Ethereum, gas price is measured in a unit of Gwei. For 5 lines of code that need 5 units of gas, this would cost 5 Gwei.
You can go to http://ethgasstation.info/ to get the recommended gas price.
How to use:
Go to the imToken transfer page, click on the miner fee, open the advanced mode, fill in the gas price (usually 20 Gwei) and gas (200000, the excess will be returned).