It doesn t explain HOW car, cdr, cons are implemented, but it does explain the details of how environments work a variable is looked for first in the local environment, then in the global one. Alternate rules for variable look-up can be used here, giving different variants of Lisp slightly different semantics. Compares the 2 pointers it is passed for equality. Each is passed a pointer to what should be a Pair. Each then returns the appropriate field of that Pair.
Cons is more complicated.
This allows even circular structures to be searched. GC then does a linear sweep over memory, adding all unmarked pairs to a new free list, and unmarking all other pairs. This is somewhat slow when Scheme executes GC, a notable pause occurs. The Lisp reader reads S-expressions and data lists from the input, and translates them into the internal list structure representation. It then uses the new global environment to evaluate the next one.