Sequence objects (also called sequence generators or just sequences) are special single-row tables created with CREATE SEQUENCE. A sequence object is usually used to generate unique identifiers for rows of a table.
The sequence name must be distinct from the name of any other sequence, table, index, or view in the same schema.
Database Designer for PostgreSQL has a simplified interface for creating auto-increment columns. Instead of creating sequences, you can simply set the Autoinc property for the appropriate column by using the Column Editor.