difference between an index and a value in haskell

I hear the two terms index and value used extensively in programming talk and know they mean different things. I'm confused, however as to what they exactly DO mean! And what the 开发者_如何学Cdifference is....?

If you have an array or a list like this:

[a,b,c,d,e,f,g,h]

then

• 1 is the index of b
• b is the value at the index 1