OK, I will like to know the billing city of the names customers please.
SELECT T1.FirstName, T1.lastname, T2.billingcity FROM CUSTOMER AS T1 JOIN INVOICE AS T2 ON T1.CustomerId   =   T2.CustomerId
billing city of the customers refers to T2.billingcity; names customers refers to T1.FirstName, T1.lastname; joining tables CUSTOMER and INVOICE on CustomerId to access billing city.