Hi. There isn't a world model editor distributed with Bridge Command 5 at the moment, but it's quite easy to add a buoy to the world model.
If you find the name of the buoy you want to add (as in the Models/Buoy folder), then use a text editor to open up the buoy.ini file in the world model.
The file looks something like this
Number=3
Type(1)="Port"
Long(1)=-4.135
Lat(1)=52.407
Type(2)="RY"
Long(2)=-4.299
Lat(2)=55.004
Type(3)="Mooring"
Long(3)=-4.505
Lat(3)=52.702
Where '3' is the number of buoys, the 'Type' is the buoy name, and the lat/long is the position in decimal degrees (North and East positive). TO find the position, you could use the scenario editor, which shows the position of the screen centre.
Have a look at the buoy.ini section of the 'World model specification' in the documentation if you want any more information, or ask here.