The maker and taker model is a way to differentiate fees between trade orders that provide liquidity ("maker orders") and take away liquidity ("taker orders"). Maker and taker trade orders are charged different fees.
A trade order gets the taker fee if the trade order is matched immediately against an order already on the order book, which removes liquidity. All market orders will execute immediately, and will be charged the taker fee. This includes conditional orders that convert to a market order, such as a stop-loss order.
A trade order gets the maker fee if the trade order is not matched immediately against an order already on the order book, which adds liquidity. You can use the Post Limit Order option to ensure that your limit order will be charged the maker fee or be cancelled.
Maker fees start at 0.16% and can go as low as 0.00%.
Taker fees start at 0.26% and can go as low as 0.10%.