A rational number is any number that can be expresses as a fraction of two integers. 3/4, 10/1, and 1763/4371298 are all rational numbers.
We might want to say that all numbers greater than 0 are rational numbers, but this isn't true. There are irrational numbers like Pi (3.14159265. . . continues forever with no pattern) and e (2.718. . . continues forever with no pattern), so we can't say that everything on the number line to the right of 0 is a rational number.
The best way to describe the set of all positive rational numbers is that they are the result of all possible combinations of dividing a positive integer (whole number) by another positive integer along with all possible combinations of dividing a negative integer by another negative integer (remember that a negative divided by a negative is a positive).