(setf arr (make-array '(2 3) :initial-element nil)) -- Makes a 2x3 array -- :initial-element is optional, the whole array is init to this value
(aref arr 0 0) -- Retrieve an array element

(setf (aref arr 0 0) 'b) -- Set array element 00 to b

(setf vec (make-array 4 :initial-element nil)) -- Makes a one-dimentional array known as a vector