Gears can change direction of rotational force from one axis to another. For example, a wind driven mill. The wind turns a shaft that is horizontal. That shaft turns a gear that is vertical, and the vertical gear meshes with a horizontal gear that turns a vertical shaft. Gears can change rotational speed. With a small gear meshed and turning a larger gear, the larger gear will have a slower RPM. Gears can change torque to increase or decrease available power. A small low force gear driving a larger gear will provide more rotational force.
Two gears rotate in the same direction when they are both either on the same side of the gear train (parallel arrangement) or they have the same number of teeth. They rotate in the opposite direction when one gear is driving another gear and they have a different number of teeth.
It depends on the ratio of the number of teeth on the two gears.
It changes the direction of movement in a gear system, so that the driver and driven gears move in the same direction.
An idler gear is a gear which connects two other gears so they will turn in the same direction. :)
Cam gears are also refered to as sprockets (just another name). A chain or belt that is driven by a crankshaft gear/sprocket turns the cam gear(s)/sprocket(s). In certain high performance applications there is no chain, there are just gears meshing but that is probably not relevant to your question.
Bevel gears can be used to change the direction of drive in a gear system by 90 degrees
In worm gears, an axle or shafts has a screw that connects with another gear. This system is used when you need to change the direction of motion and reduce speed
opposite
If the carrier is held stationary and the sun gear is the input member, the ring gear will rotate in the opposite direction at a speed determined by the gear ratio between the sun, ring, and carrier gears in the planetary gearset. The direction of rotation will depend on the specific arrangement of gears in the gearset.
A Spur gear is a gear and it can change the speed and direction of motion. You have to shift your gears in order to make your gears work. If you don't know how to, ask google or ask Wiki answers for a better answer on what to do. Remember, all gears need to be shifted at a certain period of time.
An idler gear is a gear which connects two other gears so they will turn in the same direction. :)