standard quiz and category quiz

Standard quiz - allow you to answer questions defined in the same quiz

Category quiz - this is just a placeholder. takes questions from all quizzes defined in the category and allow you to answer them randomly selected questions, upto maximum allowed limit.

Ok so i need to create several quizzes in the category before of that.

Not exactly. You can start with the very same quiz and add more quizzes/questions later.

In both quiz type (standard and category) i can set x quizzes in several pages, correct? 

But i can show the quizzes randomly only by category quiz type, correct?

Yes, you can set any number of questions in a quiz and any number of pages.

Showing random quiz is not possible though.

But i see the field to show quizzes randmly on category quiz, correct? So?

However it should very nice feature show quizzes randomly.

It's not the quiz, questions. When you are taking category quiz, you can show questions in random order.