The Addressbook.
Sorry, not yet written. I hope I will get a friend of mine who
is speaking english as his native language to translate my first german
script soon.
Meanwhile:
- 
Add a new entry using the add button and enter the data (you should at
least enter a name).
- 
Save the changes to the database (see edit->change). The changes will only
be stored if you say so. This way you can hack around without damaging
anything.
- 
If you entered an email address, you can start kmail (if it is installed) using
CTRL+M or the menu.
Missing:
- 
Any vCard support.
- 
Drag and Drop support.
- 
A lot of more entry fields.