One die has 6 numbers, 3 of which which are odd. That means each roll has a 50% chance of being odd.
To find the probability of rolling TWO odd numbers, we can multiply the 0.5 chance per roll by 2 to get:
0.5 * 0.5 = 0.25 or 25%
If you visualize the question, we have 4 possibilities:
Roll 1 is even and roll 2 is even.
Roll 1 is even and roll 2 is odd.
Roll 1 is odd and roll 2 is even.
Roll 1 is odd and roll 2 is odd.
Only 1 of the 4 possibilities results in both rolls being odd.