When writing you report, no matter what type of data you're investigating, you will need to follow the PPDAC cylce. PPDAC stands for Problem, Plan, Data, Analysis an Conclusion. Below is a guide for what is expected in each section of your report. It is split up into "needed to achieve" - things that must be in your report for you to pass, and the "ways to improve your grade" - things you can add to help get you to a Merit or Excellence.
Remember, your overal grade is also heavily influenced by how well your report is written - is it easy to read and follow? Do you use correct spelling and grammar? Do you use statistical terminology correctly? etc.
Click on the links below to see the report writing guide for the type of graph you're writing about.