Dear Peter,
Yes the override /typically/ goes in with the notes, but you can put it in different places depending on how many things you want it to effect (just the current voice, or every voice in a score with many staves for example). Lilypond often has more than one way to achieve a given goal.
When asking questions it is often a good idea to post a small snippet of code that compiles on its own, so that we can better see what you are trying to do, like the following (which illustrates how to use the snippet you took from the manual):
\version "2.18.2"
\relative {
\override TextSpanner.bound-details.left.text = \markup { \upright "rit." }
b1\startTextSpan c
e,\stopTextSpan
}
Also, do try and send replies to the whole list, so everybody can pitch in when you need help!
hth,
Kevin