Excel 2007 : Cannot create an index - need to plot house price index against time

Hi,

It's my first post, so please be nice!

I am doing a dissertation that involves looking at house prices. My simple question is this, I have 2 different data sets of house prices over time and want to make an index of them, so I can map them on a graph starting at 100%. (I hope that makes sense).

How do I create an index of the data? I have tried typing "=INDEX" but haven't managed to figure it out...?

Any help would be great and if you need clarification on anything let me know (I'm dyslexic)!