users have a table and a table of city

One city uses a lot of users. (relationship is one-to-many).

Create users:
CREATE TABLE users (id SERIAL, name VARCHAR NOT NULL, city VARCHAR NOT NULL);

Create a city:
CREATE TABLE city (id SERIAL, country VARCHAR NOT NULL, city VARCHAR NOT NULL);

How to write this sql-queries to the table referred to each other?

You would be better off with another table design. Maybe something like:

Create users:
CREATE TABLE users (user_id SERIAL, name VARCHAR NOT NULL, city_id

Create a city:
CREATE TABLE city (city_id SERIAL, country VARCHAR NOT NULL, city VARCHAR NOT NULL);

Then join based on the CITY_IDs being equal. Otherwise you would join on the City and hope that no 2 countries have a city with the same name, sorry but that does happen...

Dave