Like other graphs, they use an x axis, and a y axis. It shows how one variable can affect another, hence the x and y (independent variable versus the dependent variable). With scatter plots you can use it to find a line of best fit that shows an average correlation relationship of the data. Scatter plots also allow you to find any outliers (those little dots that aren't in a pattern, correlation, or area with the majority of other points). It usually shows a relationship between TWO sets of data. :) :>
Hope this helps! :3 :>