The Cosmic Microwave Background Explorer was a satellite back in the 1990s that measured the Cosmic Microwave Background of the universe. This CMB is the afterimage of the Big Bang, about 400,000 years after the Big Bang when the universe suddenly became transparent to photons- the earliest images of the universe we can possibly capture in light.

And it found that everything was the same no matter where you looked, to about 10 parts per million. So that is the level of variation in the density of the universe about a half-million years after the Big Bang, the differences are measured at the level of parts per million.

And then back in the 1990s the Hubble Space Telesecope took pictures of the previously most luminous galaxy ever recorded, and it was really far back in time, within half a billion years of the Big Bang. And these luminous galaxies were something that we expected to mean that they were built around gigantic supermassive Black Holes. Which means that in a very short amount of time we must have gone from "everything is the same to parts per million" to "here is a gigantic accumulation of mass concentrated in this one spot so densely that all of our models of physics don't work any more."

And so the Webb Space Telescope was built specifically to look for things in between what the Hubble had seen (in Visual Light) and what the COBE had seen (in Microwave), that is Infrared. It is designed to look for these supermassive galaxies that had Red Shifted (1) so far they had left the visual spectrum and gone into Infrared. Figuring out how all of these super luminous galaxies formed is the main question that the whole thing was designed around.

1: As things move away from us, the photons shift to the red end of the spectrum. According to Hubble's Law, things the faster something is moving away from us the earlier it is in time, and the further its photons are shifted to the right: this is why the Cosmic Microwave Background is in microwave, because it has been red shifted so far it has gone into the Microwave part of the spectrum.

It's a galaxy far far away and more importantly very very old. The image is 13.5 B years old, the photons were created just 280 million years after big bang. It's the oldest thing we have seen so far. And it looks mildly different than what we expected to see

In our current understanding of how universe formed galaxies accumulate gradually and it takes time. This one was quite large already, very shortly after the Big Bang, which is at odds with our understanding.