what does this mean"forumdisplay, showthread, standard_error find"

In the install instructions it says:

3) In forumdisplay, showthread, standard_error find:
$headinclude
Add before that:
<base href="$vboptions[bburl]/" />

what does this mean? where specifically do I find this?

thanks

[Zachery]

Edit those template, find that peice of code, add that other code above it.