For the examples below, I will use the educational database Flights.

SELECT *
FROM bookings.aircrafts

outputs all contents of the aircrafts table of the bookings schema

To output data for only a specific aircraft, use the WHERE keyword, after which a condition is specified:

SELECT *
FROM bookings.aircrafts
WHERE aircrafts.model = 'Airbus A321-200'

or

SELECT *
FROM bookings.aircrafts
WHERE model = 'Airbus A321-200'

will output data for the Airbus A321-200 aircraft

SELECT *
FROM bookings.aircrafts
WHERE range > 5000

will output aircraft that can fly more than 5000 km.

Conditions are expressions that apply to each row of the table. If for a row the expression is true, then that row will be output in the result. If the expression for that row is false, then the row is not output.

SELECT *
FROM bookings.aircrafts
WHERE 'Airbus A321-200'

will give an error, because the expression after WHERE cannot be calculated as true or false. Check:

SELECT
  aircrafts.model,
  aircrafts.model = 'Airbus A321-200'
FROM
  bookings.aircrafts

will give the aircraft models and the result of the expression aircrafts.model = 'Airbus A321-200' for each model. You see, true or false.

But if you write like this:

SELECT
  aircrafts.model,
  'Airbus A321-200'
FROM
  bookings.aircrafts

the second expression will not give us either true or false, it returns text. It cannot be used in this form in the WHERE condition.

Conditions can be more complex

SELECT *
FROM bookings.aircrafts
WHERE
  (model = 'Airbus A321-200')
  OR (range > 6000)

will output Airbus A321-200, as well as aircraft that fly more than 6000 km.

SELECT *
FROM bookings.aircrafts
WHERE
  (model = 'Airbus A321-200')
  AND (range > 6000)

will return an empty result, because we don’t have any aircraft of the ‘Airbus A321-200’ model that can fly more than 6000 km.