Why you put this: >>> before writing?

Answer 1

To tell that the code is executed in the intepreter line.

It is a tool that lets you execute single statements.
In that tool each line starts with >>>

Answer 2

You can run the same code in the playgrounds, but you need to ignore the >>>. You'll get more familiar with it when you download a Python IDE.

Answer 3

so, it's an obligation when it's a single statement?