What is the difference between the demand schedule and the demand curve? What is the difference between the demand schedule and the demand curve that a monopolist or monopsonist has? Could someone provide details for both cases or even some paradigm or a graph. I can not clarify this concepts.
Demand schedule is a table that gives you the quantity demanded at different prices.

An example of demand schedule that I found on Wikipedia is shown below:



Demand curve is a curve that plots the demand at different prices in the 2D space defined by $Q$ and $P$ (see example picture I took from investopedia below). 

Demand curve is essentially a plot of demand schedule.