The billing address is for security purposes, and games are sent by download. It's worth checking the specifications of the game page to find out the size of the game, as some games (Such as popular FPS Team Fortress 2) are quite large, especially if they are frequently updated to provide new material, bug fixes, or to accommodate DLC (Downloadable content such as extra levels that is available to purchase on some games by certain companies - You can check an individual game for DLC on its store page below the description).
The games, once purchased (Where applicable) and activated, then run exclusively through your Steam account, with updates for many games enabled by default (Though last I checked, this could be changed in the preferences).
It is worth noting, however, that unfortunately games that are purchased through Steam or use a Steam activation code cannot be sold on, however some items from selected free-to-play games (Available in the free-to-play section of the store along with other games) can be sold on the steam community market to provide "Steam Wallet funds" (Money that remains attached to your steam account) if you have made a recent purchase on the account. These funds can then be used towards buying paid games or items for Free-to-Play games.
I hope I helped a little. Sorry it's more than you need, but I felt it might help (Provided it actually makes sense).
· 6 years ago