When working with the outline, you can select any group of lines, even if they appear in different slides, as long as they are contiguous.
You might find it easier to use Slide Sorter view to perform extensive reordering, or to reorder a large presentation. Slide Sorter view gives you a lot more flexibility for drag and drop; it also shows you more of the presentation at one time.
Expanding and Collapsing
PowerPoint also makes it easy to hide all the bullets under a slide's title (commonly called collapsing the outline) or display every line (expanding). Collapsing an outline to just the titles lets you see the overall organization and flow of your presentation, without being distracted by details. Expanding allows you to work on all the bullet points, and compare them across slides. Click inside the slide you want to change (or select a number of contiguous slides) and click the Collapse button to hide all the detail, or click Expand to show all the detail.
PowerPoint does not have the capability to expand or collapse to a particular level in the hierarchy: It's an all-or-nothing setting. Either you see all the lines in a slide, or you see just the title.
If you want to collapse or expand all the slides in the presentation in one fell swoop, click the Collapse All or Expand All buttons on the Outlining toolbar.