If at any point you feel like loading up parts of your nation sheet with large chunks of information (for example a detailed description of your nation's MBT, nuclear programme, or annual cultural festival), try (do try) to put them in hiders or spoilers, so that readers (and the RPC Managers) don't have their sanity crushed under the immediate visual weight of your entire entry. If suicide becomes preferable to reading it, then you're doing something wrong.
Additionally, the term "Nation" is used here pretty loosely, and beyond any Components you choose to take there are no effective limits on the sort of nation you can have beyond your own creativity. A pan-dimensional tentacle-bodied cosmic horror whose reality-spanning appendages suffer from MPD is perfectly acceptable, provided you can fill in most of the fields. But don't do that. Please don't do that.
Population and Size: (The number of entities within your nation, as well as the area of its territory (equivalent area or volume if it's in space, sea-borne, or air-borne). On the off-chance that you're a nation of nomads or beings with no possessions or territory, or no corporeal form, Population will do. If for some contrived metaphysical reason you can't put a number on either, I'll kindly ask you to stop being difficult and move on to the next field.)
Nation Leader(s)/Authority Figure(s): (If there is no single leader or figure, you can mention individuals within the ruling group (such as a senate) or, if your nation is run in a particularly fanciful fashion, things like faceless all-powerful government departments and megacorporations)
Government: (A classification of your nation's government type (i.e. Republic, Democracy, Dictatorship, etc.), as well as a description of the nitty-gritty of government/power distribution and how things such as law-passing and day-to-day responsibilities are done. Or not done, as the case may well be. You can include radical or unusual policies and laws the administration has passed.)
National Religion(s): (What defines anything as a religion is up to interpretation, and you don't have to have one. Include Gods and Goddesses, strange rituals, competing beliefs, whatever -- go nuts. If your people don't have a national or single widespread belief system, explain why so we can all bask in your enlightenment or lack thereof.)
Major Cities: (Include a description of the Capital -- if your nation is swanky enough to have one -- along with any other cities, towns or settlements of cultural, historical, or military significance. What constitutes 'Major' is up to you and your citizens (or -- depending on your Government Style -- not), and you can include a city or population hub solely for having nice beaches or a thriving lolsorasgay scene, if you like. If you're some sort of galactic empire or space-faring nation, substitute the word 'City' for 'Planet' or 'Ship'.)
Environment: (A description of the stunning -- or not so stunning -- vistas surrounding your nation as well as any natural landmarks and locations of importance, be it in a forest, grassland, charred volcano pit or, you know, space or something.)
Technology Level: (Past-Tech, Modern-Tech, and Future-Tech are the standard ballpark classes (for around 18th-19th, 20th-21st, and late 21st century and onwards technology respectively), but put whatever you feel best describes your civilisation if you're beyond or below them. If your nation uses magic in general, or uses magic to power technology, Magi-Tech (or slightly kooler MagiTek) will probably suffice. You can give a brief overview of your nation's tech as well.)
Notable/Unique Technologies: (Anything your nation uses or has invented that counts as particularly ingenious or just generally awesome, and has put your people on the multiversal map. Save destructive and purely military tech for later. If you have magic, describe how it works here.)
Citizenry Overview: (A description of your nation's people, such as their various races/species -- however many types there are, be they bird, lizard, man, machine, or something inbetween. Like cat-people. Also include your citizenry's general outlook, attitudes, and values, should the doubtless utterly-benevolent administration allow them sufficient freedoms to actually have any.)
Cultural Overview: (The things that define your nation as unique and distinct from all those other pesky masses of people out there. Include weird cultural quirks, particular styles of dress or sayings, annual festivals and celebrations, hero worship (of your dictator or monarchy, for instance), caste divisions and class systems, and things such as that.)
Military Overview: (A description of your nation's military (if it has one), including how they're organised and trained, what kind of equipment they use (including weapons and a vehicle or two -- try not to go too crazy here) and their behaviour during war-time. If you have no conventional military, try to find your nation's nearest substitute and detail that, even if you're a technically-pacifist nation whose most devastating military manoeuvre consists of throwing harsh language and stale marshmallows at your enemies. Military and war-time technologies (like giant moon-based artillery) go here.)
History: (While a simple time-line counts, detailing some of the more momentous events that have rocked your nation (or have gone directly into its forming) will get you bonus points. Technically there are no bonus points, and they don't do anything, but you still get them.)