Function CAR in LISP program returns the first element in a list.
(car '(a b c d)) Returns a
Function CDR would return everything but the first element in a list.
(cdr '(a b c d)) returns (b c d)
There are of course many variations of this.
(cadr '(a b c d)) Returns b
Working from the inside out is the same as (car (cdr '(a b c d)))