Both TR and the documentation are right. You can first install drupal, then install Ubercart which means going to two different websites, downloading two different files, etc. etc. Of you can just do it once by using the file in the documentation which combines the two steps into one.

Whiterain,
Which two types of installation did you try? The manual and automated ways do not install two different types of Ubercart, they are two different ways to install the same thing. Maybe I don't understand the question. Which two different ways did you try?

Andy