In practice
Exchanges reward the orders that build the book and charge the ones that consume it. A resting limit order that someone else trades against is a maker order; a market order, or a limit order priced to fill at once, is a taker order.
Active traders plan entries and exits with this in mind. Entering with a limit at a level and taking profit with a limit both pay the lower maker fee; only the stop-loss, which must fill, pays the taker fee.
What to watch for
Chasing the lower fee can cost more than it saves. A maker order may not fill at all, and missing a good trade or a needed exit to save a fraction of a percent is a poor exchange.