The United Nations governs the world, I need to know how many nations are in it?

Do you know how to Google? Wikipedia has a very helpful article on the U.N.

The UN don't rule or govern the world, that's not how it works. The UN has set up a list of guide lines that a nation must follow if it wants to join the UN.

Things like human rights etc.

Also code of conduct in war.

It is more like an ethical code for contry to follow, but have no real power no army etc.

The UN was against the war in Iraq but the US and the UK went in any way.