Once your Mac boots into OS X, you'll be looking at the OS X Desktop. The figure below shows what the OS X desktop on my iBook looks like.
In addition to the desktop itself, the major components of the desktop are the Dock (the blue bar on the right side of the screen), the Apple menu in the upper right hand corner, and the Finder which is Apple's tool used to explore the computer (find files and folders). Most desktops will also show the computer's hard disk(s) near the upper right hand corner of the screen. I prefer to turn that feature off to save real estate. Here's how it looks with the computer's hard disk displayed.
Double-clicking on the hard disk icon will open it.
Also, on all the native OS X installations I have seen, the Dock is located at the bottom of the screen. I prefer to place it on the screen's right side for reasons I'll also explain later.
The icons you see on the dock represent applications that can be started with a single click on the icon. Once you do that and the application is starting, the icon will jump up and down to make sure it has your attention. Once an application is running, a small, black triangle to its right shows it is a running application. In the picture above, you can see the Finder is running (and it always is) and an application named Grab is also running.
You can also see a folder sitting on the desktop where I place materials I need to reference often or quickly. I created that folder by right clicking on the desktop. Those of you with a single button Apple mouse can Control-Click to get to the same menu.
Selecting "New Folder" now creates a folder on the desktop. It generally shows up as a folder in the upper right hand corner of the screen and named "untitled folder". To give the folder a name, simply click once in the little box surrounding the name. Notice, too, that you can click on "Change Desktop Background" and do just that. (More on that later.)