What exactly is nihilism?

I understand that it is a doctrine composed of views or beliefs that nothing has any meaning, and that what we as humans are and do has no impact on anything. There also seem to exist several types of things to dismiss under the spectrum, such as existential nihilism which I lightly describe above. There is moral nihilism which suggests that morality is just something we made up, there are many other kinds.
That’s a bit of what I don’t understand. Why so much detail on something that, in the end, says nothing has any meaning or value? It’s a little amusing.
I read a little on the history of nihilism, about how it was a thing in Russia in the 1860’s and became popular in the western world.

Nietzsche says that a nihilist judges the world not as it is but how it should be. What it seems to say to me is that nihilism is just being discontent about generally everything, so if it sucks then just bitch about it. Religion, morality, society, and their byproducts which we judge.

However, I think it is probably a lot more complicated than that, which is why I am asking. What exactly is nihilism, in a nutshell? Is it a big fancy philosophical doctrine or just an easy way to dismiss everything? Is it really associated with despondency and discontent, or is it educated observation?

Note that I am curious and not bashing nihilism, in fact from the little that I comprehend of it, my own thoughts and views on things seem to slightly revolve around it.