Re: United Nations
You have three systems in the UN.
- Secretariat - which are based in New York, Geneva, Vienna and Nairobi
- Agencies - who have their headquarters based in Geneva or New York or Vienna or Nairobi and then family duty stations (like Dubai) or field stations (like Darfur, Chad etc.)
- DPKO - Which are based in conflict situations like Darfur, Chad, Lebanon, Iraq, Afghanistan etc.
Now comes the complicated part. The Secretariat and DPKO have the same website for jobs - jobs.un.org.
You have to register and fill out the PHP on the website. The PHP is the Personal History Paper or also called the P.11.
When you apply for a post in the Field, you apply to a generic vacancy. When you apply to a position for New York or Geneva you get sent there. You do not get to chose where you can go when you first apply.
On the other hand each agency is an individual entity and has their own website like www.unctad.org or www.who.int or UNHCR Welcome etc. And their jobs are not listed together. But the guys in geneva have set up: Job Vacancies in United Nations and International Organizations to help out with all the UN jobs in all locations.
Now Healthcare is a wide ranging issue in the UN. It is all covered by UN Agencies like OCHA, WHO, UNHCR, UNFPA etc. Only UNFPA is based in New York with their large headquarters and they have a limited aspect for health care. But health care is mainly seen in field locations on in HQ. Nowhere else. Meaning you can’t do health work sitting in LA. No UN base there.
However you will do health work in Geneva or in the field or family duty station.
UNDP is by far the largest UN agency that covers everything including health care. You just need to decide on how you are going to apply.
The UN counts work experience after your masters degree for a professional post called a P post. P-2 is the entry level and requires 1 to 3 years work experience after your masters in the field you are applying for.
The UN is a huge organization and I can better help if I am provided with specific questions to answer.
Edit: As a girl your chances to get a job as a professional in the UN is higher than a man. They aim to recruit more women to keep a gender balance.