Regardless of whether an application is a word processor or disk utility, whether it came with Mac OS X or you installed it yourself, chances are it behaves in certain ways common to all Mac OS X applications. You can launch it by double-clicking on its icon in the Finder or by clicking on its icon in the Dock; it has an application menu on the left side of the menu bar; you quit it by choosing Application Name ➣ Quit (or pressing command+Q). There are lots of other ways in which OS X applications behave similarly. Here are a few tips to help you better use applications in general.
This is a bit of a rehash of information I mentioned in the previous chapters, but I repeat it here in the interest of thoroughness. You can hide the frontmost application completely by choosing Application name ➣ Hide application (or by pressing command+H). If you've used a third-party utility to add the Hide command to application Dock menus, you can also use that method.
You can minimize any window to the Dock by clicking the yellow minimize button in the upper-left corner (or by pressing command+M, assuming the developer follows Apple's application guidelines). You can minimize all windows in a particular application by holding the option button down as you minimize any window belonging to that application.
In older versions of the Mac OS, clicking on or in any application window brought every window in that application forward. However, in Mac OS X, clicking on or in an application window (including Finder windows) brings only that particular window to the front. If you want to bring all windows of a particular application to the front, just click on the application's icon in the Dock.
If you prefer the "classic" window behavior, where clicking on any application window brings all windows in that application to the front, check out Appendix A, "A Tale of Two Systems," for a few ways to bring that behavior to Mac OS X.
I've covered customizing the toolbar in my discussions of several applications, including System Preferences and the Finder. However, most Cocoa applications, and some Carbon software, include this functionality (see "The Three C's of OS X Applications" sidebar). You can usually access this feature by choosing View ➣ Customize Toolbar…. In addition, you can change the toolbar view by clicking or command-clicking on the toolbar widget/button in the upper-right corner of any application window.
One of the most under-appreciated and under-utilized features of Mac OS X is its built-in help system. Available via the Help Viewer, which can be launched from the Help menu in any application, this system provides lots of info on OS X itself, and, if the application developer has provided it, information and assistance for individual applications.
There are three ways to use Help. The first is to search all installed Help modules. Simply enter a word or words relating to the topic for which you need assistance in the search field, press return, and Help Viewer returns a list of topics, ranked by relevance (how well each item matches your search). By clicking on the column headings in the results window, you can also sort the search results alphabetically or (perhaps most usefully) by the Help module each came from. The latter is helpful for finding which results pertain to the specific application you're using.
Advanced Help Viewer search techniques: when performing a search in Help Viewer, typing a + between words will only find Help pages that contain all those words ("and"). Inserting a | between words will find pages that contain any of those words ("or"). Typing ! before a word excludes any pages that include that word from the search results ("not"). If you want to group words, use parentheses. For example: (window|menu) + application !Finder will find any page that includes "application" along with "window" or "menu," but does not contain "Finder."
The second way to use Help Viewer is to search within a particular module. Click the Help Center button in the toolbar to view the drawer of installed Help Center modules. Click on the relevant Help module (Mac Help for OS-related help, or individual application or topical modules), and use the search field in the toolbar to search within that module. (Note that for some reason, some modules don't seem to support module-specific searches—you get the same result as if you hadn't selected any module.)
The third way to use Help Viewer is to follow along with any built-in guides or tutorials the developers of an application (or the OS) has provided in their Help modules. Using Help Center, select the appropriate Help module, but instead of performing a search, use the links presented on the module's main Help page. Help Viewer will walk you through the help system for that particular module. This is an excellent way to learn tips and tricks for an application; for example, both iTunes and iPhoto have extensive Help modules with lots of tips and tricks.
At any time, using any of these techniques, you can use the Back button to go back to the previous screen(s); if you customize the toolbar with the Forward button, you can also go forward and retrace your steps. The Go menu also provides a list of recently accessed modules, as well as the results of the most recent search you performed.
If you find that the Help Viewer text is often too small, you'll appreciate the "Bigger" tool-bar item, accessible by customizing the toolbar.
This is a short tip, but an important one. One of the best ways to learn what an application can do, but one that many users never take full advantage of, is to explore the functions available from its menus and preference dialog(s). You'll often find features you didn't know existed, or realize that features you've been wanting are right there under your mouse.