The fee depends on your role in the trade (maker or taker) and your 30-day trading volume.
A maker places a limit order and adds liquidity to the order book, so the fee is lower. A taker executes an order immediately at the market price, so the fee is higher.
Your tier depends on your total trading volume over the last 30 days and is recalculated automatically. Takers pay 0.100% at every tier. As their volume grows, makers receive a rebate, which returns part of the taker's fee. See “Maker Rebates” for details.