So far I understood that anything inside quotes (double or single) would be a string to python (or any other language, perhaps).
e.g. 2 is a an interger, 2.5 is a float number, but "2" and "2.5" both are strings. So 2*5 = 10, but '2'*10 would not be a mathematical entity.
On the other hand, "hello" (with quotes) is a string while hello (without quotes) is not recognized by python. Type both hello and "hello" in python (I mean python console), you will see.
Also, str(234) would convert the no. 234 to string '234'.
Do all these make sense? This is what I understood so far, but I am not an expert on this.