If you’re new to London, follow “Trains to Gatwick Airport” signs at Victoria, London Bridge, or St Pancras

https://mariohqun142.yousher.com/southend-to-gatwick-airport-routes-costs-and-duration

If you’re new to London, follow “Trains to Gatwick Airport” signs at Victoria, London Bridge, or St Pancras. Ticket machines and staff can assist with route and fares.