Install app without using wifi or 3g

How can one install an app manually, without using wifi or 3g to download? I assume it would be possible to download the app to ones computer then connect the smartphone and copy the app to the phone, but what folder on the smartphone would the app belong in? I've tried to move an downloaded app from my pc to the download folder on the phone, successfully, but then did not see a way to open it and install it. I don't see how to access the download folder from the phone itself. Thank you.

The downloaded app is in the form of an APK file. It's a chinese dictionary from Pleco.