I have only been taking programming class (java) for a few months now, but I completely understand parameters because of it. Maybe you should take a programming class (if you are in high school). It has really helped me understand a lot about Alice because of the things I learned in the class so far, and on the other end Alice has taught me a lot about programming in Java.
I am planning on taking more advanced programming classes later on in high school and into college.
But anyway, if you really want to know the difference between parameters and variables, I guess you could just google it
Check out my best projects so far and please comment:
Tic-Tac-Toe 2.0 ................... http://www.alice.org/community/showthread.php?t=3548
Alice Paint ........................... http://www.alice.org/community/showthread.php?p=23408
Real-Time Clock .................. http://www.alice.org/community/showthread.php?p=12725
Maze Game ......................... http://www.alice.org/community/showthread.php?t=4301