Iperios is a modded Minecraft server that runs the Allthemods 10 pack on version 5.4. The whole idea is about building nations and making your own style of government.
You can start your own nation and decide your rules your laws and your ranks. If you do not feel like leading then you can just join a nation that already exists and be part of their community.
To join you first get whitelisted through their staff. New players get some starter info then a staff member helps you get going and gives you a beginner kit so you are not lost at the start.
The server expects you to have the correct ATM10 5.4 modpack installed before you join. After that you just follow the instructions from staff and then you are free to play and grow your nation.
