LEGO Digital Designer has 5 Modes 2 were discontinued.
You can Read about all the modes here.
LEGO Digital Designer:Edit
LEGO Digital Designer Mode is the first Mode that was created alongside Mindstorms and Creator.
In L.D.D Mode you don't have all the bricks made but there are some for building epic models!
LEGO Mindstorms Mode is a mode were you can build all the Mindstorms Models with all of the parts from the Sets.
LEGO Creator Mode is a discontinued mode that had all the Creator Parts with their original colours
LEGO Universe Mode is a discontinued mode that was a secret mode that was only accessed by typing the code Themeaccess=LEGOuniverse in preferences.
This Mode had all the parts that LEGO Digital Designer Extended has.
LEGO Digital Designer Extended:Edit
LEGO Digital Designer Extended Mode is the son of the mentioned LEGO Universe Mode.