1. Finder Windows programs have the task bar and menu functions located on the top of each window or panel for that program. For the Mac, they approached it differently. There's a common ribbon that runs at the very top of the screen called the Finder. This displays stats like battery life, the time, and info on background applications. It's dynamic in that the options listed on the top left (i.e. File, Edit, Help) change based on the program you have in the foreground. It takes a bit of practice to look here for options and menu settings but you'll get the hang of it pretty quickly.
2. Installing programs With a Windows based machine you simply click the executable and get presented a panel where you progress through installation. For Mac, clicking that executable loads a temporary drive on your desktop. You simply double click that drive and then begin your install. Some programs take you through a set of panels similar to a Windows machine, while others follow a more simple approach and advise you to just click and drag the app icon into the Applications folder (as shown here with Spotify).
3. Uninstalling Programs Uninstalling programs is often a breeze as well, but not always. (Ahem.… Adobe.) For most programs you'll simply drag and drop the icon from the Applications folder into the trash and Poof! it's gone. For larger programs like Microsoft Office and Adobe's Professional Suite I like to use a tool called App Cleaner (it's free). Opening that program displays a panel that you simply dump the application icon into instead of the trash. The app basically does a search for all connected preference files and caches and then gives you the option to trash those all together for a tidy uninstall.
4. Window Management In Windows there are icons on the right to maximize, minimize, and close. For Mac there are icons on the left that look like they maximize, minimize, and close as well. Except on the Mac what you may think is a maximize button is actually a fit button that is designed to size the window around the content it contains. You'll have to click and drag the panel from the lower left to make things larger. If it's an optimized OS X 10.7+ program you can click the full screen icon on the upper right of the window to enter full screen mode.
5. Command is your new Control All the shortcuts you're used to like Control + C for Copy and Control + V for Paste are on the Mac as well — you just use the Command key instead of the Control key.
6. Strange new Symbols If you're a shortcuts person, then you may make an effort to remember the hot keys to common functions. There are a few new symbols in the Mac that aren't intuitive, and you'll want to learn them. For some reason the Option symbol to me looks like the face of a person that's ummm… weighing his options (or an unimpressed McKayla Maroney).
7. App Store You may be used to going to a specific site or product page to download the appropriate Windows programs you're looking for. Or you may typically purchase something physical at a store and install using a disk. Apple is making a hard push to online distribution, and their App Store is the first place you should look for your programs. The programs sync to your Apple ID so that when you upgrade computers down the road, or simply get another, you can sign in with that ID and have access to those programs conveniently through the iCloud distribution. Some popular programs like Adobe's Professional Suite and Microsoft Office aren't in these distribution channels yet, so you'll have to resort to old school methods for them.
Those were the basics I learned when I made the switch to Mac a couple years ago. Mac users, did I leave out any essentials that stumped you?