I will guide you step-by-step on how to simply install an apk file using ADB Command.

Make sure you have setup your adb on your phone.
Visit Android Phones  and ADB access to learn how to setup your adb.
If everything is set, type in "adb install -r c:\apk folder name (directory of file)/filename.apk"
Example; adb install -r c:\systemUi.apk, this is when the apk file (systemUi.apk) is found in the c drive.