Before the James Webb telescope was launched into space, the most distant galaxy – as far as we know – was GN-z11. GN-z11 is said to have formed about 420 million years after the Big Bang. The recently discovered galaxies may have formed as early as 250 million years after the Big Bang, nearly 200 million years earlier than GN-z11.
In the video below you can see what the James Webb telescope looks like and what it is used for: