If private citizens want to be part of the solution to world problems through nongovernment organizations (ngos), they should

Private citizens can join non-government organizations (NGOs) through volunteering. Usually, different countries in the west highly support their NGOs that promote and envision the growth of their society or other societies.

Volunteer groups like GreenPeace and Housing and Development Organizations are the commonly involved groups in giving solutions to world problems. They provide the necessary service of basic commodities (e.g. food, water, shelter) for the good of many in mostly remote areas where help does not reach its way or where help is not enough. A person can easily volunteer by signing up to his desired organization that he knows would cater to the need of many.