What exactly is Steam? Isn’t it DRM?
What can I do with it?
Steam is DRM. Steam is also DRM done right.
When you “own” a game through the service, you (normally) get to install it on all of your computers for no additional fee. No questions asked. No licenses. No CD keys. Zero click installs.
Steam does many offers and offers a number of free demos. Steam also brings an actually useful in-game overlay (which, e.g., even lets you open YouTube or this site without tabbing out!). Steam finally has important social features like notifying that your friend has joined a game (and for supported games, there’s a feature to one-click-join them as well). etc.
Mind you, Steam does have some points where it doesn’t shine. My main pet peeve is offline gaming does not work if the Steam client thinks there is an update it should download and install; typically you only find out when it’s too late. A second point where Steam is less than great is that you need to own a non-free game to enable most of the social features, and they are a large part of the appeal.