GB65,
What are you trying to accomplish? I have a metric defined as RANK([Total Sales]), I'll call it [Store Sales Rank], which, when I place it on the report with Store and Total Sales (optional) metrics, will give me the ranking of that store (1,2,3...). nlim pointed you to the correct section from what it seemed like you were asking.
From your post I wanted to make sure you had actually tried the function in a metric. You did say you "looked" at it, not actually built it. I've built it and it worked for me. Below is what you'd get (you might have to play with the parameters of the Rank function). If that is not what you're looking for, please clarify. As for being an 'expert', I like helping and getting help. I sure don't know everything.
Here is what the report would look like:
[Store Sales Rank] [Total Sales]
Store
Store 101 1 $10,0000
Store 102 2 $8,500
Store 103 3 $5,000