To volunteer for community service, US citizens can serve at homeless shelters.
Community service refers to a non-paying job performed by one person or a group of people for the benefit of the community or its institutions. It may also be referred to as community payback.
It could be mandated by schools in order to meet the requirements of a class, such as in the case of service-learning or to meet the requirements of graduating as class valedictorian.
In Sweden it's a suspended sentence called "samhällstjänst" ("society service").