The rolls of the dice are independent, i.e. the outcome of the second die doesn't depend in any way on the outcome of the first die.
In cases like this, the probability of two events happening one after the other is the multiplication of the probabilities of the two events.
So, the probability of rolling two 6s is the multiplication of the probabilities of rolling a six with the first die, and another six with the second:
Similarly,
Actually, you can see that the probability of rolling any ordered couple is always 1/36, since the probability of rolling any number on both dice is 1/6: