Its a variable that can hold more than one value.
Say you have an amount of gold you win after each level of fighting. First you'd create the array
DIM goldAmount(50)
(50) means there are 50 slots within the variable goldAmount, you could use this as each level.
Then you'd assign a value to each slot:
LET goldAmount(1)=10
LET goldAmount(2)=15
LET goldAmount(3)=20
LET goldAmount(4)=25
etc...
So when you beat level one, you get 10 gold, level two, 15 gold and so on.
LET level=3
LET playerGold=playerGold+goldAmount(level)
Whoops, you beat me to it, but I have a question also, how are arrays saved to a file?