Ninja world is basically lets see:
Battle arena is almost like arcade mode, training fights etc, where you beat on one another in fight after fight with no really concequences.
Ninja world is like open play story mode. The ninja world is where you venture out and build on your bio telling it's story. The content is saved. You do missions and gain kumi (used for buying abilities) and Ryo (used for buying nw related stuff). You can form a clan or join and village, claim land, fight other clan's or villages for land. It's literally called The Warring States Era (WSE for short).
So the basics of it is this. The NW is split into land marks. These are like mini states that make up a nation (fire nation etc). Each land mark has been made as a thread. We have an interactive map which shows you this:
https://animebase.me/pages/map/
Scroll over some of them if you can, but if you click on a landmark it takes you to the thread. Thank
@Jas for that.
Some land is coloured, this is because those landmarks have been claimed by clan's or villages.
How do you travel though?
You can only travel to an adjacent landmark. You post in each thread as you go, marking out your journey and what you're doing.
You have to wait 45 minutes to move to the next landmark each time.
This means that if you're not careful, someone can attack you, though this would lead to a fight etc...
You start off where ever you like, but for you it would be best to start in your village, build up with them, bit of protection for you too.
From here you're out telling your story.
THis has been a quick run down, but here are the full rules:
https://animebase.me/threads/ninja-world-guidelines-and-rules.757182/