Having never done it as part of one such group, I don’t know exactly what goes on, but essentially there’s a large body of literature on leftist political concepts, covering the ideas of why anarchy rather than archy, how to practice it, how to organise etc. I’m definitely the wrong person to explain it, generally socialists (at least here) are the ones doing all the reading, I’m a lot more interested in praxis tbh.

Some classic anarchist writers include Kropotkin, Bakunin and Proudhon. But the communist and socialist literature often applies too.

The anarchist library has lots to browse and the anarchist faq is a great starting place despite its huge volume of content, I highly recommend casually browsing it.