The basic concepts of Lisp are easily mastered. Some computer science
courses don't "teach" Lisp at all, but allow the students
pick it up from class examples. Most of the work of mastering Lisp
comes from learning the large libraries of
utilites available to Lisp programmers.
This website gives information mostly about Common Lisp. (See also, related languages.) This site gives listings of books, reference material, and other resources. There is a also a guide to Lisp programming style which comes from the Lisp FAQ (a listing of Frequently Asked Questions, and their answers).
To get your feet wet, here's some classic code:
(write-line "Hello, world.") ;Print the famous greeting. ;;; A function to produce the factorial of an integer. (defun factorial (n) (if (= n 1) 1 (* (factorial (- n 1)) n)))