If you're like most Mac users, you probably don't give your keyboard much thought: You press a key, it relays that key-press to your system, and that's all there is to it. But there can, in fact, be much more to it, if you take avantage of OS X's support for multiple keyboard layouts.
When you initially set up your Mac, the OS X Setup Assistant gives you the option of choosing a default keyboard layout. Many users never deviate from that initial choice. You can, however, choose a different keyboard layout any time you want. For instance, if you're composing in French, you might be better off using AZERTY instead of the standard QWERTY. Same goes for composing in non-Roman alphabets, such as Chinese or Russian: You can switch your keyboard layout to any number of those. And many users prefer to use the Dvorak (or other alternative) layout for more efficient typing.
Whatever your reason for using an alternative keyboard layout, you can do so by opening the Keyboard pane in System Preferences, choosing the Input Sources tab, then clicking the Plus button at the bottom of the left column. From there, you can search for and add whichever layout(s) you want.
While this process is fairly straightforward, it can get a bit cumbersome if you need to switch layouts regularly. To make the process faster, once you've added your desired keyboards, check the Show Input Menu In Menu Bar option in the Input Sources tab. That done, you should see a flag or input icon in your menu bar; clicking on that will let you select the keyboard layout you want.
You can also switch between these input sources using hotkeys: Go to the Shortcuts section of the Keyboard system preferences, select Input Sources (which only appears if you've enabled more than one keyboard layout) and then check the box next to the hotkeys. Note that those shortcuts may by default be set to Command-Space and Option-Command-Space — which are also the default hotkeys for Spotlight. So you might need to change them. (You could try Control-Space and Option-Control-Space, instead).
If you find yourself needing to switch between layouts regularly, then you might enable the option to Automatically Switch To A Document's Input Source, which is also on the Input Sources tab. With this feature enabled, changing the keyboard layout will only do so for the currently active document. That means you can switch away from that layout when you switch away from that document, using your main layout on other documents and in other apps. But when you go back to the document, then the keyboard layout you were using with it will be re-activated.
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