APK stands for Android Package (sometimes Android Package Kit or Android Application Package). It's a type of file, such as an MSI for Windows or a DMG for Mac, that contains the code and resources of Android applications. It's often referred to as an application, but it's actually more like an application container. This is because it contains all the elements that an application needs to be properly installed on your device.
To install an APK file, all you have to do is open the browser, find the apk file you want to download and tap on it. You can then see it downloading to the top bar of your device. Once downloaded, open Downloads, tap the APK file, and tap Yes when prompted. The application will start to be installed on your device.
Bluestacks is a popular tool for both Windows and Mac that is designed for Android applications to run on PCs and Macs. It's a safe and legitimate way to open APK files. When the application is ready for shipping, Android Studio compiles it and then places it all in one container: an APK. If you want to open an APK file on Windows, you might need a cross-platform product like Bluestacks or Android Studio.
APK files are intended only for Android devices and that's why you can't change them directly to a file that you can run in another framework. APK files can be dangerous, especially if they request permissions to record your personal data, control device settings, or perform tasks (such as calling or texting your contacts). To ensure safety when downloading APKs from sources other than the Play Store, select your preferred browser (Samsung Internet, Chrome or Firefox) with which you want to download the APK files. Now, find the folder where you downloaded the APK file and copy it to the appropriate location in the folders on your device.
You can use Google Play Store to install apps and games, or you can cancel the pre-order and install the APKs yourself. If you want to get the APK version of an application that you have previously installed, you can use AirDroid from the Google Play Store. While you can use Android without learning the meaning of APK, studying a bit will help you understand and appreciate the platform even more.