After picking the map type of your preference, turn your attention to the top bar with all of the icons and numbers.
From left to right:
Three blue-clad men - Manpower: The number of able-bodied men ready for military service. Used to recruit new troops and let damaged regiments regain lost men
Scale - Stability: How stable your country is. This effects the overall revolt risk, tax modifier, and other stuff. Goes from -3 to +3. - is bad + is good. Read the guide titled "The Invisible Fortress" for more info on Stability
Stack of coins - Money: It's just money. You use it to buy things.
Red crown - Prestige: AAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
Red flag - Infamy/Reputation: Indicates how aggressive you are. The higher you go the harder things involving other countries gets. Diplomacy gets harder, gaining support in the Holy Roman Empire gets harder, becoming Papal Controller gets harder, and your merchants aren't well-received in foreign ports. If you go over the limit, everyone will hate your guts and people will just start declaring war on you to wipe you off the map.
Squid Girl's father - Merchant: You send them to trade centers to bring in ducats. They have a percent chance of a successful successfully competing in that trade port. The percentage is affected severao factors.
Indiana Jones - Colonist: You send them to non-wasteland grey provinces. Each colonist is worth 100 population by default (more if you changed the setting in the options when selecting a country). Once the area reaches 1000 population either by constant bombardment by colonists or by population growth after sending in a colonist or 9. Colonists are also used to take land from horde nations (Golden Horde, Nogai, Timurids, etc.) after conquering provinces. More on that later
Diplomat: These are used to interact with other countries. Used for anything from declaring war to calling another country's ruler a ♥♥♥.
sodomite You can also marry that ♥♥♥
Missionary: These are used mostly to convert heretics and heathens in your provinces (either conquered from heretic/heathen lands or conversion due to protestant reformation). Religious ideas also use up missionaries.
Sagat from Street Fighter II - Spy: Spies are used to cause ruckus tuckus in other countries. The most fun use for them is causing nationalist or patriot revolts on other countries. They can be used to bribe defenders to speed up a siege, assassinate an advisor, or get a casus belli on a chosen nation. Some options are only available when a spy is used on the capital of a country.
Magistrate: These are used for building, most provincial decisions, most national decisions, cultural decisions, and other decision stuff.
It tells you the date. If you click it you pause the game. Plus and minus speed up and slow down the game.