Extensions add features to PostgreSQL: uuid-ossp for UUIDs, pg_trgm for fuzzy search, and postgis for geographic data. Install with CREATE EXTENSION name. List installed extensions with SELECT * FROM pg_extension.
Useful Extensions
-- List available
SELECT * FROM pg_available_extensions;
-- Install
CREATE EXTENSION IF NOT EXISTS "uuid-ossp"; -- UUID generation
CREATE EXTENSION IF NOT EXISTS pg_trgm; -- fuzzy search
CREATE EXTENSION IF NOT EXISTS postgis; -- geo data
CREATE EXTENSION IF NOT EXISTS hstore; -- key-value store
-- Use UUID
SELECT uuid_generate_v4();