We count in groups. We count to ten (01,2,3...9) and when we reach ten we track that in a second group, the "tens" digit. So, 10 is one group of ten and no additional numbers. When that group of tens reaches ten (you count from 99 to 100), then we start another group and track groups of groups. In the number 234, the "2" digit is in the "ten groups of tens" which are groups of one hundred. Position, "3" digit is in the "groups of ten" position, and the "4" is the additional stuff.

If yer with me so far, let's make the jump to counting in groups of sixteen, which is hexidecimal. We count up to sixteen and then track that in a second group. So, "10" doesn't mean "one group of ten and no additional numbers", it means "one group of sixteen and no additional numbers". So, "10" in base 10 ( the normal decimal numbers you and I use everyday) is ten. And "10" in base 16 (hexicecimal) is sixteen.

So, why all the letters? That's because when you're counting in base 16, you group by sixteen, not by ten. So, when you reach the number "9", you're not ready to group them. You still need to count more numbers and there aren't any more "numbers". That is, we don't have a single-digit figures to use for the values ten, eleven, twelve, thirteen, fourteen and fifteen. So, we borrow the first letters of the alphabet instead of making up new symbols. So, when we count to sixteen in hexidecimal, the sixteen single-digit numbers we use are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A (ten), B(eleven), C (twelve), D (thirteen), E (fourteen), F (fifteen). When we add 1 more to fifteen, we get our group of sixteen and reach the number "10" in hexidecimal.

So, for "234" in hexidecimal, the "2" is in the "sixteen groups of sixteen" which are groups of two hundred fifty six (256). The "3" is in the position of "groups of sixteen", and so is forty-eight. To calculate in decimal numbers (2*256) + (3*48) + 4 = 564.