Multiple styles of doorknobs are available, but they all perform the same basic function--allowing access through a closed door. Some doorknobs work in conjunction with keys, while others simply act with the part of the door that keeps it shut.
Doorknobs consist of only a few parts, but they are all essential to its function.
The external parts of a doorknob are those that are used to unhinge that which has kept a door from opening. On either side of the door, a knob is placed.
Typically, one of the knobs has a locking mechanism, while the other side has a key hole. If unlocked, turning either side's knob--generally in either direction, clockwise or counterclockwise--enables access through a doorway as this unhinges it.
The only other externally visible part of the doorknob is the stem, which is what surrounds the spindle and connects the knob to the base.
Spindle and Screw Posts
A doorknob looks simple on the outside, but there are long screw posts within. Two or three screw posts connect either side of the two knobs to each other internally.
In the very center of the doorknob is the spindle, which is what enables you to turn a doorknob. If a doorknob has been locked from one side, the spindle is actually what becomes unable to turn, thus making it impossible to turn the outside doorknob.
The inside knob with the lock won't function until the entire doorknob has been installed, but it will only function once the spindle from the outside doorknob has been adjoined to it.
The dead latch is a small piece of metal that springs back and forth from the side of the door whenever the knob is turned. It only sticks out about an inch, with one side flat and the other curved.
This dead latch is actually what keeps a door closed when the doorknob is not in use, confining itself into the small hole in the strike plate next to the doorknob. It will always stick out unless the door knob is turned, at which point it retracts into the door, which is accomplished by the spindle snagging the device as it turns, thus pulling it in away from the wall.