If you mean from purely technical point of view, you:
1) Identify functional requirements
2) Develop the features that you need
3) Deploy the modifications
4) You import master data that you need
5) You add users to the system
6) Users start using the system
This process is the same no matter if you use the system only in one country, or roll out to multiple countries. So just repeat these steps for each country. And this process is practically the same for older AX versions and D365FO.