what is the imporantce of port cities in the Caribbean?

Answer 1

Same as port cities in all places. They provide a place to park boats.

Answer 2

Well, ships reaching there from far, had to get food, water, medicine, tools, etc., ..
Thus around any port cities were founded to support and service the port! In other areas, like in Mediterranean, ports were made to support the cities (trade materials, etc.)!