The Arrange features have been available for as long as I can remember. They've always been accessible via the "Window" menu, as shown in this CS2 screenshot:
In the modern interface (CS4 and 5, and Elements 8 and 9) they're still in the Window menu, but also much more accessible right there at the top of the screen. It's a handy little button that you might not have noticed much before.
Here it is in Photoshop:
And here it is in Elements:
When you click on that, you get this:
All those little shapes are the various configurations into which you can arrange your windows.
As people upgraded from their earlier versions to one of these modern versions, it was not uncommon to see laments on forums about how they didn't like the new "docked" windows. They missed the ability to move their windows around as they pleased. Well, the truth is, these little buttons make window distribution much easier and faster than it ever was before.
Let's take a look at them. The most obvious one (and the default setting) is the first one - "Consolidate All":
That's where you can see one photo at a time. It fills your screen, and any other windows are behind it, accessible by their tabs. You can flick through the images by pressing Ctrl Tab (I'm not sure what the Mac equivalent is, sorry).
But when you want to see more than one image at once, those little buttons become very handy.
They're pretty self-explanatory as soon as you start playing with them, so I'll just discuss the ones I use most. First, "Tile All in Grid":
This is a beauty. It does whatever it needs to do to show you all your images at once. If, for example, I have eleven photos from a set open, that button distributes them all like this:
I know what you're thinking ... "You can't see what they are!" Yes, they're not fitting their new windows particularly well, are they? Don't worry, there's a neat trick for that, too, which I'll discuss in a moment.
The other common situation is where I just want to see two photos side by side. That's where the "2 up" buttons (either horizontal or vertical) are useful:
They split the screen to show me two images at once:
By default, it divides my screen evenly. But I can change the balance any way I want. All I need to do is grab the bar between the windows ...
... and move it where I want it:
This is useful when I'm editing one photo, and using the other for reference.
A couple of things to mention. If you have a split screen like this, and you open a new file, it will open in a tab to share the window with your previously selected image. If you would like to view all three images at once, choose "3 up" from the Arrange menu. Or, if you'd like to move an image from one window to another, simply grab it by its tab and drag it across. And when you want just one window again, choose the "Consolidate All" button.
That's all very well, but you might be wondering when you'll use these functions. I can think of three important applications.
The first one I mentioned a few sentences ago - comparison while editing. If I'm editing a set of images, and I want them to be consistent (consistency is hard, isn't it??) I'll edit the first one, then keep it open in a small window, whilst I edit each of the others. By continually comparing my edits back to the first photo, I ensure a standard result across the set.
The second application is somewhat related to the first - transfer of layers. If I've edited one photo from a set, it is often handy to apply the same adjustment layers straight to the next photo. This can save a lot of time. So I make both photos visible, select the edited image, then go to the Layers Panel and highlight the layers I want to transfer. Drag and drop - done!
The third application would be when assembling collages or storyboards. It might suit you to have all your images open and visible, to easily choose/copy/paste onto the layout. I don't really do much of that kind of work, so I don't speak from vast experience in this regard.
Ok, I've rambled on about all the little icons long enough ... what about the other options?
"Float All in Windows" is like the old "Cascade" option. It "un-docks" everything into floating windows:
This will suit those people who are still pining for the old ways, but once you are comfortable with the modern interface, you won't bother with it much.
To dock all the floating windows again, simply choose any of the Arrange icons, and they'll jump into place for you. "Consolidate All" is the usual method, of course.
"New Window" is an interesting one, and I could write a whole article on it by itself (maybe I will!). It makes a new window which is an exact "live" copy of your current image. At first glance it looks like you've duplicated the image, but no - it's still the same image, but you've now got two views of it. If you do something to the image in one window, you'll see the same adjustment appear in the other window. I believe high-end retouchers use this so that they can be doing close-up dodge-and-burn work in one window, and be watching the effect on a zoomed-out view in the other window. Play with this function, because it might be very handy to some of you.
"Actual Pixels" and "Fit On Screen" also appear in the View menu. The former gives a 1:1 (zoomed in) view, and the latter is meant to zoom out to fill the window precisely. In my CS4, "Fit On Screen" doesn't work if I have a split screen - I'm not sure if this is a bug in my system, or if other people have the same issue.
The "Match" options are handy. Remember this?
Sure, all my images are visible on screen in their own windows, but they're so zoomed in that I can't really make out what they are. All I need to do is select one, zoom out a bit so I can see it at an appropriate size, then choose "Match Zoom". Bam! All the other windows will zoom out to the same size, and instantly I have a better view of my selection of images.
"Match Location" means that if I am viewing the bottom right hand corner (for example) of one image, that function will instantly let me see the bottom right hand corner of all the other windows as well.
And, of course, "Match Zoom and Location" does both.
That's about all there is to tell you. I hope this explanation will help speed up your workflow a little.