If you haven't already, download and install the appropriate version of QGIS for your machine from http://www.qgis.org/.
Note that new versions of GGIS are usually released every few months - it's not normally necessary to upgrade, although new features are added all the time. New versions are installed as a standalone application, so you can have more than one version installed if you like.
A couple of tips to get started once you have QGIS installed.
Settings > General > Icon size
Settings > Locale, then check
Override system locale, and choose the locale to use (you will need to restart QGIS to see the effect)
Digitizing in this exercise
Layers for normal work