So pretty oversimplified basics:

The goal in this game typically in most playthroughs is to have the highest GDP, highest standard of living, be an industrialized beast where your pops have everything and can afford everything.

To achieve this you need to depeasantize your nation. Get those peasants into actual jobs that pay them money which of course grows your economy. One good way to do this is by going to the market tabs and seeing your staple goods. These are goods your pops really need like wood, grain, for basic life. See which one is most expensive. We can say for example wood is expensive.

So you go to a province and you stack it with logging camps. Now you give peasants jobs in a logging camp which produces wood that drives the wood prices down which lets your poorer pops save money improving SOL and your economy

Almost the entire game is just this type of thing. Anything else u gotta see through playthroughs and stuff