Hi,
From the docs: the mapcar function "Returns a list that is the result of executing a function with a list (or lists) supplied as arguments to the function"
So, assuming lst is equal to '(1 2 3 4 5 6 7), (mapcar 'list lst) returns: ((1) (2) (3) (4) (5) (6) (7)) because it returns a list that is the result of executing the list function to all items in lst.
Which is equivalent to: (list (list 1) (list 2) (list 3) (list 4) (list 5) (list 6) (list 7))
Same thing for: (mapcar 'list (cdr lst)) which is equivalent to (list (list 2) (list 3) (list 4) (list 5) (list 6) (list 7)) and return ((2) (3) (4) (5) (6) (7))
When mapcar is called with more than one list, the supplied function (list function here) is applied to all corresponding items of the lists while none of the list is empty.
(mapcar 'list lst (cdr lst)) is equivalent to: (list (list 1 2) (list 2 3) (list 3 4) (list 4 5) (list 5 6) (list 6 7)) which returns ((1 2) (2 3) (3 4) (4 5) (5 6) (6 7)).