Do a salary employee has to make overtime, without pay?? my boss ask employees with salary to come on saturday, but due they are with salary and not paid by the hour they don't receive nothing when they come on saturdays! It this fair? It is legal??

Salaried is only a pay method. What matters is whether your job duties classify you as exempt or non-exempt. The extremely large majority of people who are exempt are paid on a salaried basis, but there are a few exceptions; likewise while most non-exempt employees are paid on an hourly basis, a non-exempt employee can be paid on a salaried basis as long as they also receive overtime when it is due.

An exempt employee has no legal expectation of overtime, ever. There are no circumstances whatsoever in which an exempt employee is legally entitled to be paid overtime, regardless of how many hours they worked. An exempt employee is paid on the basis of getting their job done, not on the basis of their hours. If an employer chooses to pay additional compensation, that's fine; they can do so, but they are not required to do so, ever, unless the employee is operating under a bona fide contract that says otherwise.

A non-exempt employee MUST be paid overtime for every hour over 40 that they work in a work week. (In a very few states, an employee must be paid overtime for every hour over 8 in a day, but that is the exception rather than the rule.) This remains true regardless of whether they are paid for the first 40 hours on an hourly or a salaried basis.

It is an employee's job duties, not their job title and not how they are paid, that determines whether or not they are exempt or non-exempt.

Barring a few industry specific exceptions (and some of these exceptions are further state-specific) again barring a contract that says otherwise, either an exempt or non-exempt employee can legally be required to put in extra hours and/or to come in on Saturday. The only difference is that IF those extra hours put them over 40 in a week, the non-exempt employee must be paid overtime and the exempt employee does not.