Let's look at the first two paragraphs of my sample answer for the question below.
The graph below shows the amounts of waste produced by three companies over a period of 15 years.
Introduction (paraphrase the question):
The line graph compares three companies in terms of their waste output between the year 2000 and the year 2015.
Overview (two main / general points):
It is clear that there were significant changes in the amounts of waste produced by all three companies shown on the graph. While companies A and B saw waste output fall over the 15-year period, the amount of waste produced by company C increased considerably.