The items in a pair/cons are selected by the
built-in procedures car and cdr.
(car (cons 4 5)) ⇒ 4
(cdr (cons 4 5)) ⇒ 5
The strange names are left over from the early days of Lisp.
If you don't like them, make your own names:
(define first car)
(define second cdr)
(first (cons 4 5)) ⇒ 4
(second (cons 4 5)) ⇒ 5