It's the refueling that potentially gets a huge usable payload to the Moon. A second Starship whose only payload is fuel would launch with the first and they'd rendezvous and transfer fuel. Ostensibly if something went wrong with the refuel rendezvous the payload (or personnel) carrier would still be able to abort back to Earth.
https://www.nasa.gov/history/diagrams/apollo.html
1: https://www.nasa.gov/wp-content/uploads/static/history/diagr...
That was a concept called "Earth Orbit Rendezvous" which was discarded early on during the Apollo program in favor of "Lunar Orbit Rendezvous" where the Command and Service Module (CSM) and the Lunar Module (LM) was launched on a single Saturn V. You can see this in the movie Apollo 13.
What? Have you watched any Apollo mission media ever?
Watch Apollo 13 the movie at least and get the most basics of facts straight.
Starship gets refueled in orbit (by a fleet of Saturn V-class rockets). A Saturn V could put about 8 metric tons on the lunar surface. With refueling, Starship can land 100 metric tons on the moon.
SpaceX plans to stretch the second stage to increase fuel carrying capacity for tanker flights, so the actual number is TBD until both the revised Starship and its engines (Raptor 3) are built and tested.