A lot of students seem to be worried about pie charts. Here are some questions to get you thinking about how to describe them:
What does a pie chart always show?
Yes, pie charts always show you percentages because the whole "pie" is always 100%.
Are pie charts used for comparing?
Yes, you can compare the percentages/numbers within a pie chart, or you might have to compare between 2 or more pie charts. "Comparing" will be the main focus of a pie chart task.
Do pie charts show changes (increase, decrease)?
You can only write about increases and decreases if there are 2 or more pie charts and they show percentages for different years (changes over time).
What verb tense would you use to describe pie charts?
Yes, past simple when past years are shown, or present simple if no years are shown.