For Hundred or Hundreds?

Both the words 'hundred' and 'hundreds' are correct. As a noun 'hundred' means ' a number equal to 10 times 10'.. Being a noun plural form is 'hundreds'..But simply ' hundred' is also acceptable.. You can say ' three hundred' or 'three hundreds'..

Is it 2 hundred or hundreds?

hundred without a final “s” on “hundred.”Hundreds (of…) can be used if there is no number or quantity before it. Always use a plural verb with hundred or hundreds, except when an amount of money is mentioned:Four hundred (people) are expected to attend. Two hundred (dollars) was withdrawn from the account.

What is the difference between hundreds and hundred?

That is correct. In compound numerals, 'hundred' and 'thousand' stay invariable: three hundred, two thousand nine hundred etc. The plural is only used to show a large but approximate quantity: hundreds of people, thousands of cars, hundreds of thousands of ants etc.