Here's what a commercial license allows you:
- when you buy a commercial license in a country you automatically get a new warehouse in that country
- you can use this new warehouse to move your goods from one country to another
- you can access the national markets (goods, construction, transport, energy, ...) of the country
Then you just have to click on the Buy button and choose the country.
The price of commercial licenses is set by the government (therefore by the players) of each country.