What is a convection oven?
Without a convection setting, your oven heats from the bottom up. This fills the oven with warm and cool air, making it difficult to cook food evenly. If you've ever had to turn your cookie tray to get everything evenly browned, you know what I'm talking about.
On the other hand, ovens with convection settings have a fan and exhaust system that moves hot air around your food, allowing your food to cook evenly and quickly. Because the exhaust system pulls air out of the oven, excess moisture that has built up in other ovens is removed, browning and caramelizing your food while keeping the interior moist.