Does their organization really serve a good purpose, or are they just useless?

I have studied a lot of their peacekeeping mission and feel like they don't do shit. They just kind of send soldiers from around the world to watch people die and not really protect them, especially its big failure to stop Rwanda's genocide in 1994 and Bosnia's massacre in 1995

They are really serving as a purpose in terms of uniting the world under one stronghold. Kofi Annan (I don't know if he is still the leader of the organization or not) has been at the epicenter of politics in the entire world, enforcing rules to help make countries form a truthful bond. Ever since his resignation, the United Nations continued to do their jobs significantly. They indeed do have a purpose.

The concept of it is good but it's never gonna work, if they tell America or some other big superpower country to not invade such a country and they do it, what are they really gonna do to stop them? nothing because they aren't powerful enough and losing one of those countries would hurt the UN more than it'd hurt a super-power country.

They're good for ending small conflicts and whatnot but they're not good enough for what they're originally intended to do and never will be.