Is it true that veins have valves that help keep the blood flowing in the correct direction? 

Veins are the blood vessels that carry blood back to the heart from the rest of the body, and their walls are much thinner than those of arteries. Veins have valves that prevent blood from flowing backward, they help ensure that the blood flows in only one direction, towards the heart. This helps to maintain the flow of blood back to the heart, even against gravity, and supports the overall functioning of the circulatory system.