Samsung Galaxy SIII has come with some useful pre-loaded applications--you can said Messaging apps, Phone apps, Contacts apps, etc-- that you can use directly without having to install them first. But, as with other Android phone, the Samsung Galaxy SIII also allow you to install another apps, either from its official market or non-official sources.
1. Google Play Store App
This is the official market for all Android phone and you'll find this apps as one of the stock apps inside your phone. Here you can download and install either free or paid apps. To make you be able to access the Google Play Store and another Google services, make sure you have activated your Google account on your phone.
See also:
How to Access Google Play Store
2. Samsung Store App
This is the second official market for Samsung phone and you'll also find this apps as one of the stock apps inside your phone. As same as the Play Store apps, this apps also provide you with a free or paid apps. Create your own Samsung account to allow you accessing Samsung Store app and another Samsung services.
See also:
How to Download and Install Apps on Samsung App Store
3. Google Play Store Website
You may noticed that this way is similar with the first ways I've mentioned above. Yes, thanks to Google cloud-based system which will allow you to install apps remotely to your Android phone from Google Play Store website through your Computer or Laptop. This way of course will extend your convenient of searching and browsing the apps in the Play Store. All you need is login into the Google Play Store website using a Google account associated with your phone.
See also:
How to Install Apps Remotely through Play Store Website
4. Sideloading Apps directly through the Phone
Aside from installing apps from the official market, you can also install apps from another sources, or users usually refer it as install .apk file. Apk is android packaging file or it's the same with .exe file in the Windows Operating System. This of course will useful if the apps you want to install is no longer available on the Play Store or Samsung Store, such as Adobe Flash Player. However, by default this option is disabled for security reasons. If you want to enable sideloading apps, you need to enable
Unknown sources option that you can find under security settings. Once you've enabled this option, you can download a .apk file through your phone's browser apps then open it through the Download app to start installing. You can also download .apk file from your PC or laptop then copy the file to your phone and open it with the My Files app to start installing. This way also allow you to install from another third-party apps store, such as Amazon App Store, Humble Bundle Apps, and else.
See also:
How to Install .apk Files
5. Sideloading apps from PC
This way will allow you to install .apk file from the computer, with or without connecting your phone to the computer. AFAIK, the available option to do this way is by using ADB or use AirDroid app--tell me if you know the other ones--. If you use the ADB, you need to connect your phone to the computer by using USB cable and enable
USB Debugging option on your phone. While if you use AirDroid app, you need to connect your phone and computer in the same network.
See also:
How to Install Apps using AirDroid App
Well, these are 5 methods that you can do to install the desired apps into your precious Samsung Galaxy SIII. However, if you have another way to install apps and it's not listed here, then I'll really appreciate if you willing to share them through the comment below :)