How do I use a cell reference within a cell reference?

Here is what I want to do. 

I want to return a value from column B but the row number will be dependent on what the user enters into cell F5, for example.

So instead of =B5 or some other specific cell in column B

I want column B and whatever value is in F5 for the row number. so =B&F5  

So the reference is to cell that is column B but variable to whatever is in cell f5