Install the APK
By default Android will block the installation of non-Play store APKs. They do this to prevent any malicious apps from being installed under your nose. So first we will tell android to allow apps from unknown sources. To do this, go to Settings > Security > Unknown sources
Now we will use your file explorer to navigate to the saved APK and launch it.
If you are overwriting an existing app like I am here, hit Install again.
If the app is compatible with your device it will install just fine from this point on.
And that is how you sideload an app onto your android device. The best part about this is your device does not need to be root or modified in any way. Everything will work right out of the box.