Think of it this way,
players is a list, let's say it currently looks like this:
NPC Code:
GuyA
GalB
GuyC
GalD
GuyA is position 0, GalB is position 1, and so on.
eg:
NPC Code:
0: GuyA
1: GalB
2: GuyC
3: GalD
An index essentially the
position in the list. (Usually -1 since most lists start from a 0 based index, as does Graal)