When describing pie charts it is often necessary to consider comparison vocabulary and numbers in terms of percentages & proportions. A single pie chart only provides information about one particular moment in time. Therefore, unless you have 2 or more pie charts, your overall comment will not describe a trend over time.
A good place to start with an overview of pie charts are these short videos from the ESL 4 Free website & Education Wisdom (use the forward keys on the control bar on the you tube ink to go to videos 5 & 7)
Attached under Materials below is an example worksheet, which includes the tasks on identifying the important information you need when analysing a pie chart; examples of relevant vocabulary; a model answer gap-fill exercise.
The following websites provide good explanations & example of how to organise a pie chart description. They can be found under the category heading of Writing Task 1 (on the right hand side of the blog). Road to IELTS is under the Multi-Skills category.
1. UGRU Level 3 Writing: Choose the button Pie Charts & Tables
2. Dominic Cole’s Blog: Examples and a tutorial training video are provided.
3. Essay Builder: Model descriptions are provided.
4. Writefix: click on the US Spending Patterns options.
5. Road to IELTS: Choose the Writing option & then Practice Zone. Have a look at the following:
(i) Set 1 Task 1 dealing with numbers
(ii) Set 9 Task 1 %, fractions & ratios
(iii) Set 10 Practice 1