In the UK, we are often told to use the STAR technique in job interviews when answering this type of question. This means that you briefly explain the Situation overall, what your own TASK was in addressing that situation, what Actions you took, and what Results you achieved. The purpose of the technique is to focus on what you yourself specifically did instead of speaking generally about what your group or company did. It gives you a framework in which to highlight what initiative you showed, how you went about achieving the task, and what the results were (hopefully positive!).
So for example, perhaps your community had a lot of litter and your school was asked to help clear it.
Situation = the amount of litter is growing, it is unhealthy and unsightly. My school was asked to take part in a clean up programme.
Task =I was asked to organise my classmates to clean up a specific neighbourhood.
Actions = 1. I addressed my class describing the issue and led a discussion on how we could tackle it. 2. I organised the students into teams and assigned areas. 3. I obtained tools and bags 4 5 6 and so forth.
Results - I managed a four-hour clean-up period on a Saturday, significantly improving the appearance of the neighbourhood and reducing health risks for inhabitants. The local community leader contacted our school principal to say thank you for the dramatic improvement.