Short question but would require a rather long answer
I can give some examples though, for instance every nation has a tag. Prussia has PRU. If you wanna create a scenario with Prussia, but more powerfull, you could copy your Grand Campaign. eug file and rename it to Prussia. Open it and change the tag SWE to PRU... delete all other tags/nation descriptions. At the bottom you can se that it says
include = "scenarios\1492.inc" change it to
include = "scenarios\prussia.inc"
Then copy and rename your 1492.inc file, rename it to prussia. Open it and you will search for the tag PRU
country = {
tag = PRU
Somewear under it you can see
ownedprovinces = {
290 }
controlledprovinces = {
290 }
nationalprovinces = {
289 290 }
It shows the id number on the province/provinces you own, controll and have as core provinces. (If you open the province file in the Db directory you have all the provinces id numbers.) If you wanna grant Prussia more core-provinces just add some numbers, if you wanna add a province you have to do two things 1. add the number in both the owned and controlled rows 2. copy the province to under your nations description in the inc file. For example if you wanna get Danzig from the start. Find out what Danzig have as id number, write it under your own nation, delete it from Poland and copy paste the province description from Poland to your own.
A province description looks like this (Prussia (id 290))
city = { fortress = { level = 1.000000 }
population = 15000
location = 290
capital = yes
}
The "capital = yes" means it has the capital, if you add, for example shipyard = yes it will contain a shipyard also.
Note: It is important that you delete a province description witch you have added somewhear else..there can only be one nation who has just that specific province...
Then there is lots morte you cand o when creating a scenario but this is the basic stuff
