What is diffrence between these two? Is it important?

Question

Type "d",'d'

It gives:

('d', 'd')

But

"d"+'d'

Gives

'dd'

Answer 1

I'd say that their only difference is, that you necessarily need to escape double quotes in double quote strings, and single quotes in single quote strings.
" ' " Valid
" " " Invalid
" \" " Valid
" \' " Valid

' " ' Valid
' ' ' Invalid
' \' ' Valid
' \" ' Valid

Answer 2

This is a contact of strings, they are glued together if in quotes.

Answer 3

In Python, you can choose freely between ' and " - it both turns out as str.