I'll start by saying that no world war will happen. At least not due to this current conflict.

The conflict between Russia and Ukraine dates back to many years ago and before anyone starts pointing fingers, I think it's best to understand what led to the Russians attacking their neighbor.

The situation is quite unfortunate. It's not a full-blown war yet, but people have died and that's saddening.
Looking at the facts on ground, the Russia's action is a bit justifiable even though I feel they should've pursued diplomatic paths instead. Nevertheless, the deed has been done and I wish they quickly come to a quick resolution so as to put an end to the killings.

And the UN?
I think people oftentimes over imagine the role of the UN in the international community. The UN is more or less and observer in matters like this. It's an oversimplification, but that's the best way I can put it.
The only thing they can do is just t try to bring both parties to the negotiation table.

No outside country will send troops to aid Ukraine. This isn't 1939. The most they can do is impose sanctions.

If Nigeria supports Ukraine, it won't really matter much because we're not part of the big guys that matters. But it might affect our relationship with the Russians in future.

If a world war does miraculously happen, it won't reach the shores of Africa. That, I am sure of.
The effects will though. Because a war of that magnitude will collapse the world's economy. So, how can you be safe? Have money. Enough money.