The gear which is attached to the pedal with the larger […]
The gear which is attached to the pedal with the larger diameter is the driving gear. Now, this year drives the rear gear with the smaller diameter. And hence the gear at the rear tyre is the driven.
Driving gear is the gear which have to transmit power to other gear, it is the source of power transmission and cause of rotation of the other gears. And the gear which is rotated by the rotation of driving gear is driven gear power is obtained at driven gear.
The "driving" or drive gear is the source of power or rotation. The driven gear is turned or moved by the drive gear. Example: The pulley on a motor is the drive pulley and a pulley on a pump is the driven pulley. Example: The pinion gear in a differential is the drive gear and the ring is the driven gear.
Depends. It may be pressed onto the motor’s shaft, or the shaft may have a keyway and a straight or Woodruff key, or the shaft may be D-shaped and the gear held in place by one or more setscrews, or the shaft may be knurled, or the shaft may be plain and featureless and the gear held by one or more setscrews, or the shaft may have a drive tang which fits a slot in the gear, or the shaft may have a square end which fits a square socket in the gear, or the gear may have a pair of mating tapers which clamp the shaft. There are many other driving means, but these are the most common.