There are lots of them. Have you tried some reading on the 'Net?
Some obvious ones to the user:
Cost of License: $$$ vs. 0
Filesystem layout: c:\ d:\ e:\ etc. vs /, /var, /usr, /home
Appearance of UI: Strictly controlled vs. heavily customizable
But computers are so complex, there are thousands of things to learn about each, and way to many to list here. Use Google, find some articles and read up. 😉
(* yah, yah, mostly "strictly controlled" if you don't know HOW to customize your Windows ).