Dedoimedo posted a short tutorial explaining how to install the Steam platform software in Ubuntu 13.04 family

All right guys, you sort of know how this task goes. I have already shown you that in my Beta version review, as well as in the followup guide, which focused on the release of the official version of the Steam software for Linux. However, things are ever so slightly different this time around, and I would like to give you the most accurate, up-to-date instructions to how you can enjoy your games on Linux. While this tutorial is mostly applicable for Ubuntu and family, it should serve you well on other distributions, too.

  How to install Steam client in Ubuntu 13.04 - Tutorial