A Wish List is a list of products (and quantities thereof) that you have your eye on. Maybe it's all the necessary parts for a project you're building, or maybe it's a random assortment of favorites that you always want to be able to quickly access.
As many as you like!
A public Wish List can be viewed by anyone. Anyone can then add those products in those quantities to their cart and buy them at any time. Even though it is public, the contents of your Wish List can still only be edited by you.
If your Wish List is set to public, feel free to give out the URL to your friends, family, robotics group, LUG - anyone!
Click on the Wish List you'd like to edit to view the contents of that list. From that page you can change all aspects of the Wish List, including its name, what's on it, and whether it's public or private.