Rather than having a single lever or button as you'd find on standard toilets, a dual-flush toilet will usually have a system with two buttons or levers, one for solid waste, and one for liquid waste. Dual-flush toilets also have a larger trapway (the hole in the bowl) than a standard toilet, and use a different system to flush waste than standard toilets do. Dual-flush toilets are much more efficient when it comes to water use than standard toilets, but they're more expensive, and solid waste can leave streaks in the bowl.
Standard toilets use siphoning action to remove waste. When the toilet if flushed, a large amount of water fills a siphon tube and pulls the waste down the drain. In a dual-flush system, water pushed down from above pushes the waste into the drain. The larger trapway makes it easier for waste to be flushed down the toilet, and reduces the chances that the toilet may clog.
The dual-flush toilet is also very efficient in removing liquid waste. While water in the toilet tank is used to flush away solid waste, only the low amount of water that stays in the bowl is used to remove liquid waste, reducing the amount of water that's used. Due to the option of being able to choose how much water you use to flush away waste, dual-flush toilets can save up to 68% more water than standard low-flow toilets.