Re: why cant i open downloaded files on my android phone and tablet?
If he came from Google Play, you're fine.
If you didn't install it, it can't run.
.apk are Android apps
You need to have file manager and "enable showing file extensions"
Computer Basics 101 so you can ask and folks can understand and respond.
Downloading games from other sources not Google is how computers, smart phones and tablets, get infected with junk, adware, malware, redirected to harmful sites and such. Pop-up ads you can't dismiss or get rid of.
And those .Exe files that run on Windows platform.