How can you install Steam games offline?

You cannot install a Steam game offline. It needs to connect to the Steam servers the very first time to confirm you own the game.

If you do not want to redownload the game, go online, click install, let it go as far as where it starts downloading, close Steam completely and copy the files from the SteamApps folder on another machine, then launch Steam again. However, this process still requires an internet connection on first play.

Steam has an option to "Backup local files" or similar you can use on a game. It saves all the downloaded information for the game in a convenient file you can move around and restore on another computer. However, I believe steam will still demand to connect to the internet before you can play the game for the first time, or possibly at all.