How does the useSession hook in TanStack Start works

I saw it one of the examples and would like understand how it works. There's no docx for it.

import { useSession } from '@tanstack/react-start/server'

import { useSession } from '@tanstack/react-start/server'

import { useSession } from '@tanstack/react-start/server'

import { useSession } from '@tanstack/react-start/server'