Android application package (APK) is the package file format used by the Android operating system for distribution and installation of mobile apps and middleware.
APK files are analogous to other software packages such as APPX in Microsoft Windows or Deb packages in Debian-based operating systems like Ubuntu. To make an APK file, a program for Android is first compiled, and then all of its parts are packaged into one file. An APK file contains all of that program’s code (such as .dex files), resources, assets, certificates, and manifest file. As is the case with many file formats, APK files can have any name needed, provided that the file name ends in “.apk”.
There are many sources of APK files across the web, but be sure to choose a site which you trust. Some APK files may contain malicious software (malware) which could compromise your phones security, so it is best to be cautious before downloading or installing any app from outside of the Play Store (and even in the Play Store you’re not completely safe!). Generally speaking, APK files found on sites like XDA should be safer to download than from elsewhere, but read some reviews and user comments before downloading or installing an APK.
When you want to install an APK manually, just open the APK installer app and navigate to the folder where you have your APK files saved. Now, simply click on the application to bring on the installation screen. Click the install button to successfully install the application.