In one of my first posts I mentioned that a lot of people think their documents or photos are stored within the programs that created them, so that for example their Word documents are actually accessible only from within Word. But they're not. You can store your files in lots of different places on your computer - on the desktop, in your My Documents folder, or even in a folder you create. So it's important to understand how that process works. It helps to think of your computer as an electronic filing cabinet. In a physical file cabinet you can have lots of file folders, and each folder can have many different kinds of stuff in it. Same thing with computer files. You can put different file types in a file folder, so that a single folder can contain documents, photos, audio files, video files, spreadsheets and on and on. You can even "nest" folders, putting lots of folders inside other folders. Folders are just a device that help you stay organized. You can name them anything you want, and you can store them anywhere you want.
Both the Windows and the Mac operating systems have programs that let you visualize the contents of your computer. The Windows program is called "Windows Explorer" (not to be confused with Internet Explorer, which is their web browser, and I'd love to talk to the nitwit that named it that). The Mac program is called "Finder". They're different in looks, but they both do the same thing - allow you to keep track of where your files are.
Here's a Windows Explorer window:
And here's a Mac Finder window:
For now, ignore the stuff in the left-hand columns and focus on the stuff to the right. Those rectangular icons (yellow in Windows and blue on the Mac) are supposed to look like manila folders. If you click on the plus signs (Windows) or arrows (Mac) next to any of the folder icons the view will expand to show the contents of that folder. In the image below you'll see that I've expanded the Mac's Pictures folder to show that it contains .jpg files, a .png file, a PDF file, a .pxm file and a bunch of file folders :
Some of these files were created by the Photoshop program, some came directly from my digital camera, the .pxm file was created by the wonderful Pixelmator image editing program, and one file I downloaded from the web. If you were to click on the little arrows next to any of the other folder icons they would expand in the same way and you could see what files (or other folders) are stored in there. The point is that I put those files in there, not that they wound up there automatically.
You can create your own folders any time you want, using the File menu in Finder or Windows Explorer. You can store your files in any folder you want. You're not stuck with the "default" location that your Word or other program chooses for you. All you need to do is choose the location you want when you save and name the file, using the Save As command in your File menu.