First, you need passion and drive to want to help others. Willingness to travel to places in need of help, and be able to offer people whatever they need, is very important.
Start volunteering at various organizations, hospitals, etc. to give yourself a feel of what the job would entitle, as well as a background in helping others.
College is not necessarily something needed to help others, but it could be helpful.
Someone interested in the welfare of the planet, and wants to protect the environment would benefit from taking a Geology course.
Sociology and psychology are also great Majors for those wanting to help people. It will give you the information you need on different areas you will be helping, and how to accommodate to specific area's and people's needs.
You're considered a Humanitarian just by donating money to help fun relief efforts of those that travel to help those in need, like various Celebrities and people involved in Politics.
To find different area's that you can work in, visit http://www.reliefweb.int and go to "Vacancies" to find a complete listing of Jobs around the World.