Factbook - Think of them as an official international article about your nation using most objective data possible. You can think of it as a Wikipedia page type of thing.
Overview - It is rather sparse information about your nation. Preferably keep it short. It is usually clicked by the people that want quick information on your nation without much reading. It is an invitation to read the rest of your factbooks and it can have links to your most interesting Accounts.
History - Every important event that happened in the past and your overall timeline should be written in a factbook in this category.
Geography - Everything about your country's forests, mountains, cities and maps should go here.
Culture - This is where you should keep articles about your national language, ethnicity, folklore and such.
Politics - This category is for all the stories about your votes, important political campaigns that have impact on your people and all current politics that is not legislation.
Legislation - From the constitution to the most ridiculous laws of your nation state.
Religion - Here you can post articles about religion of your citizens including all religion that does not exist in the real world.
Military - Most agree that you should put military operations here as well as a description of your army and its equipment, as well as possible laws regarding them.
Economy - All the things regarding money that are not taxes, because that would be legislation. You can also write down your most influential companies here, or worker unions.
International - From international foundations similar to the red cross, all the way to military alliances and federations, but only if all other nations included already agreed on being part of it, otherwise post on the Regional Message Board (RMB) or send them a Telegram.
Trivia - Useless information that you find interesting about your nation.
Miscellenious - That's just a very fancy way of calling it "other".
Account - It's a non-interactive story from the reality of your nation. If no other nation can have any say on the matter, then it's best to put it in an Account and only share a link to it in the RMB.
Military - Stories about your soldiers and such.
Trade - All stories about international and national transactions.
Sport - Stories about sporting events, fan fights and such.
Drama - Personal stories of regular civilians that happen to shake the nation and make "drama".
Diplomacy - All stories about things that happened in embassies and dignitaries from different nations that visited your country, or your people visiting other countries.
Science - Stories about your scientists and their discoveries.
Culture - Those may vary from descriptions of operas, tv shows to cultural festivals.
Other - Any story that is interesting, happening in your nation, but does not fit in any category.
Regional Message Board - RMB is for things that need discussion with other nations from the region and at the same time need publicity, with the possibility of other region members joining into the discussion.