Belize City is the largest city in Belize. It is located on a small peninsula protruding into the Caribbean Sea. It was the capital city until flooding and other damage from a hurricane prompted the government to relocated to Belmopan, nearer the geographic center of the country.
The international airport (Philip S. W. Goldson International Airport) for Belize is located in Belize City. Philip S. W. Goldson is about 30 minutes drive from Belize City's center. The best way to get to and from the city center is with a taxi. Although an airport bus service exists, it is very infrequent and unreliable. BZE (Philip S. W. Goldson International Airport) is served by most major US airlines (American, Delta, United, and Southwest) as well as a couple regional carriers (Honduras, Maya, and Tropic).
As a visitor to Belize, you'll almost certainly have to spend a little time in Belize City, whether you like it or not. The international airport is in Ladyville, at the northern edge of the metropolitan area. Belize City is the transportation hub of the country, and most flights, buses, and car rentals originate here. If you're arriving late or leaving early, you'll have to overnight in or near the city. Make the best of it. Take care, but explore and enjoy the city.