From BlenderWiki

[edit] What can I do with Python?

You can use Python to create scripts to manage various tasks. Python can be used to make tedious tasks easier. You can program new features you need or use scripts that are already available. Python support is not limited to that though. You can use it to program IPOs with PyDrivers (http://blender.org/cms/Python_Scripting.763.0.html). Also fields are evaluated by Python so that you can input calculations directly to any numerical input field in Blender.

[edit] How do I execute a Python script?

Open the script into Text Editor Window and hit alt-p. Alternatively you can copy the script into your scripts directory defined in Blender's settings and then update scripts menu. You can do that in Blender's Scripts Window.