Welcome to Android Central! If I understand correctly, you have a PC with a broadband connection via Ethernet but do not have a home wi-fi network set up, correct? And you're trying to install apps onto your tablet, which presumably only has wi-fi capability but no mobile data (i.e., 3G or 4G), right?
You're going to be pretty limited in this respect. You could potentially download an .apk file (installer file) of an app to your computer, then transfer it to your tablet via USB connection, where you could then execute it to install. However, the source of .apk files is not always trustworthy, so you're more liable to install a virus or other malware as well. These sources may also offer .apk files of apps that were intended for purchase, which is obviously illegal.
Unfortunately, I think Kevin's suggested link above, although a good one, won't work for you if you don't have a wi-fi network set up.
Having a tablet without a home wi-fi network severely limits the tablet's usability, so I would strongly suggest buying a cheap router (you can get decent ones for about $20) and hooking it up to your broadband modem to set up a network. Otherwise, consider going to your nearest Starbucks and using their wi-fi to download and install those games from Google Play. Good luck!