In this lesson I explained why I only recommend using shows, illustrates and compares in your task 1 introduction. There are plenty of other synonyms for the word "shows", but almost all of them will look strange in the context of a description of a graph or chart.
One other possibility that I also occasionally use is the phrase "gives information about". Look at the introduction below, for example.
Click here to see the task. Here's my introduction:
The bar chart and pie chart give information about why US residents travelled and what travel problems they experienced in the year 2009.