The included presets give a great overview of what you can do with FabFilter One. You can either use the presets as they are, or tweak them further to create your own unique sounds.

The preset button shows the name of the current preset. If you've changed the preset by adjusting one or more knobs, the name is dimmed to show that this is not the original preset.
The Default Sound preset is loaded automatically when FabFilter One is started. To change the default sound, simply overwrite this preset.
Next: Saving presets
See Also
Using FabFilter One
Creating sounds