Those errors are because Terraria_Server.exe's reference in the project is incorrect. You need to change the reference to it in the project. Look here for more info.
Ok I click "Add Reference" and choose "Terraria_Server.exe" and it didn't take away the errors.
Fixed it. All I had to do was delete the original reference then re import the terraria_server.exe and then the errors went away.
I looked at the example and I have absolutely no idea what's going on -_-
my main concerns are with
A) The "AddCommand" bit. How do I make it accept a number?
B) is the ".Calls" what performs the action?
C) What are all the Access levels? like AccessLevel.PLAYER?