Note: please see here for an animated visual of how left/right joins work.

SELECT * FROM customers
LEFT JOIN orders
    ON customers.id = orders.customer_id;

SELECT * FROM orders
RIGHT JOIN customers
    ON customers.id = orders.customer_id;    

SELECT * FROM orders
LEFT JOIN customers
    ON customers.id = orders.customer_id;    

SELECT * FROM customers
RIGHT JOIN orders
    ON customers.id = orders.customer_id;