You start out playing as a tiny icon.
A icon are 16 x 16 pixels and is called *.ico.
*.ico is also a derogatory word which grown *.icons might call each other if they're pissed.
Like calling someone kid.
Your first mission is to head to a CLASS-registry within HKEY_CLASSES_ROOT. There you'll find information about each file extension, and what's required to become that specific file extension.
It could be storing specific data, painting a picture, or just walking around exploring The System.
If you want to see what kind of file-types there are, go to your start-menu, hit Run and type regedit.