"Don't worry, I have a PhD in applied physics"
Thrusters provide basic force in a given direction, and are only activated when the movement key is pressed that corresponds to the direction they are facing (relative to the pilot; the thrusters that begin facing forwards will be the ones to respond to forward controls, etc.). Each successive tier of Thruster has greater thrust, with armor increasing in smaller and smaller percentages at each successive tier. Every second tier also has a larger footprint, making them difficult to replace when adding new Thrusters.
Thrusters are primarily used to propel hovercraft and land vehicles beyond their normal maximum speed while improving acceleration. The smaller, lower tier thrusters are also useful for improving turning characteristics on all classes of vehicles, they are especially important at improving pitching on small aircraft with less than five wing surfaces. However, more thrusters does not necessarily mean more speed, since the faster a vehicle moves, the more air friction the vehicle is subject to. This effect is particularly visible on aircraft, which can fly at almost the same speed with four or eight thrusters per arbitrary amount of weight. The acceleration, however, is always improved with additional thrust, however, additional thrusters allow damage to be sustained without penalty to the user, if all thrusters are well placed.