There are many organizations that are looking for people to volunteer or even work full-time for free in their overseas locations. Some of the organizations focus on relief work while others are charitable or religious organizations. It is best to begin by looking for an organization that is well-aligned with one's interests and beliefs and then begin the work of figuring out when and how it might be possible to work abroad for free. Each organization functions slightly differently and it is important to research this as well before making a commitment to work abroad for free. Also, the exact financial agreement for volunteers and full-time workers should also be well understood before embarking on the journey.
Programs that ask people to work abroad for free vary in terms of what they can provide for their workers. In some cases, travel, food, lodging, and basic needs are all covered by the organization. In these cases, the workers are not receiving a salary or even a stipend for their work, but they also are not expected to pay their own way. However, there are other organizations that ask volunteers to both work abroad for free and pay their own way. This is a big difference in terms of the financial investment that workers may or may not have to make in their efforts to work abroad for free.
For people who are not interested in making much money or saving money while they work abroad for free, the first scenario described above may be ideal. It is best to have at least a small amount of money saved for items and incidentals that may not be covered as part of the worker's room and board package. The second scenario is really only right for people who have the means to pay for all of their own travel, food, accommodations, and anything else that they might need during their time abroad.
It is important, when preparing to work abroad for free, to fully research one's destination. Learn as much of the language and customs as possible before departing. Also, be sure to find out what kinds of medical precautions are necessary to take before embarking on the trip and while traveling abroad. It may be necessary to be vaccinated before leaving to work abroad for free. Be sure to talk to a medical professional about this well in advance of the departure date.