There are some major and some minor changes in the upgrade from 2.x to 3.x.
Python 2.x: print ‘Hello World’
Python 3.x: print(‘Hello world’)
Python 2.x: print(7/5) output: 1, print(-7/5) output: -2
Python 3.x: print(7/5) output: 1.4, print(-7/5) output: -1.4
There are so many more, go ahead and explore them in depth. Here's a tutorial series you can refer to.
You can check out this video to get started with python.