With this dialog you can customize your ship to many degrees. Staterooms and low berths may be added and removed. Fuel space swapped with cargo space. Hardpoints and mounted weapons may be changed. Even the jump drive, maneuver drive, and power plant of your ship. Lastly, you can choose the conduct your annual maintenance. This is normally done once a year, but if you have been running on unrefined fuel, you might choose to do it more often.
All shipbuilding rules are from the original Classic Traveller. Consult those manuals for details.