Character constants need single quotes.
Use: INSERT INTO users(user_name, name, password,email) VALUES ('user2','first last','password1', '[email protected]' );
See the manual: postgresql.org/docs/current/static/…
Note: After I encountered the same problem and almost missed the answer that exists in this page (at the comments section), thanks to @a-horse-with-no-name – I’ve posted this answer