So you have a result set... it looks something like this
city | team
----------------
chicago cubs
ny yankees
boston red sox
If you ask for the city of row 0, you'll get chicago, of row 1 you'll get ny, and so on. It's for results that return multiple rows. If your result only returns one row, then you'll always use 0.
(If you're using multiple rows the manual suggests using a fetch to get the whole row at a time rather than using the random access)