What is the different between in-place operator and variables in python

Answer 1

You are comparing two completely different things here:

In-place operator is also about variables. It's just another way to change the value of a variable.

x = x + 2

Here we create a new value from x + 2 and then give it the name x. (The old x is lost now.)

x += 2

Here we change x directly.

Answer 2

variables are identifiers used to refer to some memory emplacement...

in-place operators are shortcut to assign result of operation between at least one variable and some expression (with or without variable)...

my_var = 36 # simple assignement
my_var += 6 # same as my_var = my_var+6