So suppose our string is a DNA sequence and
we're going to call it dna and we close it in quotes.
So here's our sequence, a's, c's, d's and t's.
Now we might want to get just the first character of that string.
So then we use this square bracket operator.
We put it next to our variable name.
So DNA zero, that's going to give us the first position in the string.
So that position there, that zero, is called the index.
And there's a funny thing we do in Python programming, and in most programming
languages, and that is, we start indexing things with zero rather than one.
So, we're used to talking about positions in lines or queues or
whatever as being one, two, three.
So you might think that the letter g is the first letter in this string.
And it is the first letter in our normal way of talking about.
But in Python, it's the 0 with letter.
So the first position of the string is actually position 0.
So if I get position 0, I'll get the letter G out of that.