Here's a press release from the resolution. The "Transatlantic Slave Trade" as a proper noun refers to the historical kidnapping and taking of Africans to the New World to be enslaved.

The resolution emphasised “the trafficking of enslaved Africans and racialised chattel enslavement of Africans as the gravest crime against humanity by reason of the definitive break in world history, scale, duration, systemic nature, brutality and enduring consequences that continue to structure the lives of all people through racialized regimes of labour, property and capital.”

It doesn't enforce reparations, but:

It affirmed the importance of addressing historical wrongs affecting Africans and people of the diaspora in a manner that promotes justice, human rights, dignity and healing, while emphasising that claims for reparations represent a concrete step towards remedy.

The US objected:

Furthermore [per the ambassador], the US “does not recognise a legal right to reparations for historical wrongs that were not illegal under international law at the time they occurred.”

I'll note for thoroughness' sake that it not having been illegal under international law is basically true but 1000% beside the point (obviously). The US Supreme Court actually heard cases in the early 1800s about how slavery was treated under e.g. the Law of Nations, but evidence was scant that it was prohibited, and the court more or less (oversimplifying) had to make shit up. The important point is that you can't say "Oh, well the perpetrarors collectively didn't prohibit it, so there are no grounds for reparations." It's obviously ridiculous.