Contribution to community means extracurricular activities. Things your child can do can be volunteer work, school newspaper, school year book, sports that your child can compete in, music that he can perform for the school audience. All these are things that you child can contribute to the community.
You don't need to worry too much about this until your child goes to the school. When your child is there, he should consider joining different activities.
If you are filling out your application, it probably means what your child would like to do at the school.
