The thing you can do is to find lots of charts and graphs from magazines. Pick one and write a report or description of its “main points”. Give your report and 10 of your graphs to a friend or family member: if they can tell which graph you are writing about in only 3 minutes, then you have done a good job of describing the main points. If not, think about what was missing
You’ll see in the assessment criteria that an overview is “necessary” at band 6 , a short summary of all the main points