differences between rails 2 and rails 3

I am planing to follow project based ruby on rails book to learn it. I
wonder if what kind of differences there ara between these two
version. Are there lots of syntax and usage diffs? I will use rails 3
environment to my ubuntu. thanks

Yes, there are many differences. Make sure that the book or tutorials
you follow match the version of rails you are using (at least the
first two digits anyway).