A trade order gets the maker fee if the trade order is not matched immediately with an opposing order already on the order book.
When using a Limit order, this is where you choose the price that your order will execute, thus, incurring a maker fee. This would be the opposite of a Market order, where you accept the best available price, and thus incur a taker fee.
Limit orders can still execute as market order if the price you select is not placed on the correct side of the order book, read here on how to set your price for a Limit order.
You can use the post limit order option to ensure that your limit order will be placed in the correct side of the order book, and get the maker fee, or else it will get cancelled. (No order is placed at all)