Europa Universalis IV

NOTE: Due to the ongoing additions and changes to the game mechanics, the info on this page may become outdated over time. A detailed beginner's guide can be found at the EU4 wiki: https://eu4.paradoxwikis.com/Beginner%27s_guide

Trade is obtuse, but the basic idea is to use merchants to forward trade from upstream to your capitol node (or some other node you are collecting trade in). Each node in the upstream chain gets a multiplier for forwarded trade, so having a lot of trade power in a series of linked nodes, and forwarding it all means you invent money out of thin air, and it adds up. The default setup for most countries works well enough, so until you want to play with it, you can just leave it like that and forget about it entirely.

Setting a rival makes it cheaper to demand stuff from them in peace deals, makes your spies (f.inst. diplomats fabricating claims) harder to detect, and will earn you an "Enemy of Enemy" relation bonus with their other rivals (+1/month up to +20). They will of course hate you for it.

The "Improve relations" advisor not only make improving relations faster, it importantly also makes negative penalties that decay, decay that much faster (such as "aggressive expansion" from grabbing a lot of provinces quickly). On the topic of AE: Be careful with it. It stacks up quick and can take a long time to go away again.

Admin power is probably the most valuable of the three types, since it is used to unlock idea groups and increase stability.

When choosing idea groups, be aware that you need more points to unlock the sub-ideas. Try to pick a category where you will have points to spare. It is, generally, a poor choice to pick a Military group as your first pick, since you gain much more by just straight up teching up military a few times early.

France is unfair (or easy-mode if you play as them). They get big armies, their traditions make those better and they have insanely good leaders. By the middle of the game, they can take on the rest of Europe and stand a decent chance at winning. Turning off "Lucky Nations" takes their (and a few other powerhouses, like Austrias) I-Win button away, but they remain a challenge.

The Ottomans is a good starting nation for a first game. They have a decent army (but are held somewhat in check by a few of their neighbours), interesting events and some options about which direction to expand in.

Other than that, pay attention to the tooltips. A lot of info about mechanics is hidden in those.

Castille is also a good nation for starters. If you get good relations with Aragon, there's a high chance to get an event that downright gives all of their shit to you. (The gist of it is that either you need rulers of opposite genders and they don't have a heir during the 15th century, and during that whole century the chance has an effect of triggering, but no longer afterwards.) Castille is also neat because if you get cordial relations with France you basically don' thave to care about much invading you at all and you can work on uniting the peninsula and/or colonising stuff.

Don't reload when you lose a war or territory. Setbacks are very common when the AI decides to gang up on you for some reason. Just truck on and keep dicking around for a century or so and then change to another country until you get the gist of the mechanics.

Expanding is a lot more focused on warfare than CK2, and there's a deeper combat system. Getting generals is very important because they make a huge difference.

As for strategy, the simplest thing to do is waltz your massive doomstack into their doomstack and chase it a bit to completely thin them out, preferably destroying the whole thing. If they're fighting on your ground, it's easy, but armies defeated in their homeland will automatically quickly retreat to the furthest province in the realm. So smashing an Ottoman army in Tunis might make them waltz all the way to the Caucasus if they have a massive empire spanning North Africa, for example.

A bit more advanced, but remember that outright annexing provinces is costly and it will take a long time to fully convert their culture and religion if you have to. The most practical way of defeating an enemy is to force them to release vassals, and then working your way on diplomatically annexing them, or even better, annex territory, release that territory as a sovereign state and then start integrating them into your realm. It sounds roundabout, because it is, but 50 years to fully annex your vassal and get cores on them is a lot more practical than annexing the territory and getting rebels for 150 years while you slowly and costly put cores on their provinces.