In order to initiate a remote download you need to make sure that you are logged into your Steam account on the computer you wish to have your game installed on.

After this you need to do the following to download a game:

Login to your Steam account via http://www.steamcommunity.com Click on Games Click on All Games Locate the game you wish to download and click on the download button

You will be able to see the progress of the download until it is complete. Once finished you will be able to return to your PC and play your game.

Note:This is currently not supported on the Steam Mobile App.