Can someone give tell me about what diplomats do and any major requirements?

Answer 1

Diplomats represent their country in foreign countries in various fields. Some are "political Attaches" and analyse the political affairs in the country, others are "Cultural Attaches" and arrange cultural tours of their own nationals to the country they are working in. Military Attaches analyse the military situation within that country and often liaise with them, especially if there is fighting in that country. Consuls look after their own citizens in the foreign nation.

Diplomats range in status from menial positions through to "secretaries", Attaches to "Amabassadors" who run the Embassy.

Answer 2

Here is a very useful link that will give you all the information you need.
http://careers.state.gov/officer/index.html

As for what you should major in, most people will tell you you should study international relations, political science, and languages. This is simply not true. Once you have passed the foreign service exams, you will be taught any skills or languages you need for the assignments you are given.