Oxygen blocks are available when you enable you website as a design set. Block categories that Oxygen comes with are ok, but could be more specific or specialized. Enabling Custom Block Categories allows you to set new categories, which will also show up in your design set when imported on another site.
To use, simply modify or remove the existing block categories, add your own, and order them how you want. Want to reset to defaults? Delete all of them (click all the "x" icons; hint: start at the top) and save to restore the defaults.