Gamersgate is actually my favorite download and DRM system of the various DD services.
Basically, entering your username and password on the site allows you to access your game page. It has an entry for each game you've bought, showing the Box, Product Key, and links to the installer, any patches, and a pdf of the instructions. The installer handles everything else, eventually giving you a box to copy-paste the Key into. Beyond that, there's nothing to worry about. The game is just installed on your computer and functions like any other game with a no-CD patch.
By my understanding, you don't even need to GIFT it to your mom. You can create a username and password, buy the stuff, then give the username and password to your mom to access the downloader.
EDIT: Like Frag said, the downside to GamersGate is that downloads take 3~4 times as long as they would take on Steam, at least with my connection.