How does negative feedback differ from positive feedback and...?

Usually, negative feedback is more common. Negative feedback functions to prevent something from being overloaded by decreasing its content and vice versa. For positive feedback, a substance is produced even more if it has already existed. For example, when there is too much sugar in our blood, insulin will respond by converting the glucose into glycogen while increase the metabolic rate. This is to decrease the sugar content, thus, negative feedback. For positive feedback, when a woman is on labour and she has to contract her cervical and uterine muscle. The existence of prostaglandin and oxytocin induce the contraction. Their existing amount stimulates more of them being produced. Hence, more contractions. This is positive feedback.

Negative Feedback is constantly occuring to maintain homeostasis, positive feedback however often occurs due to large homeostatic changes. I cannot recall what hormonest exactly (mabye progesterone), but Positive Feedback is important during pregnancy.

When the fraction of the output of an amplifying device fed back to the input has the same phase as the input signal, i.e. the feedback reinforces the input signal, it is called a positive feedback. When the feedback opposes the input signal, it is a negative feedback. The negative feedback is much more common and has some distinct advantages such as reducing distortion etc.

Perhaps the actual query is in the latter part of the question. Sorry, I have no ideas on this subject.

Negative feedback is when the effect caused by a stimulus tends to reduce or eliminate the stimulus.  For example, your house's thermostat has a negative feedback function.  When the house is cold, the thermostat measures it, notes that the temperature is below the set point, and turns on the furnace to heat the rooms.  (So, the stimulus of the temperature being low is removed.)  This is usually used in homeostasis, which is the process of maintaining relatively constant physiological conditions in the body.
Positive feedback is when the effect caused by a stimulus tends to increase the stimulus.  An example is the milk let-down reflex in nursing mothers.  The baby suckles, which triggers the release of the hormone oxytocin.  This causes the milk to flow.  The baby drinks it, and suckles more, so more hormone is released, and more milk is released (etc.).  The body uses a positive feedback cycle occasionally, when it wants to make a change relatively rapidly.