Creating public variables

I am trying to create a code with the following variables and I receive this message when compiling: The type or namespace name ‘Tile’ could not be found. Are you missing ‘UnityEngine.WSA’ using directive?
how do I fix this and what is ‘UnityEngine.WSA’?

public Tile[,] tiles;
public Tile border;
public Tile grass

Dear Trobbit,

I assume that the Tiles you want to create are images / part of your game.
Then you should not use the “Tile” type.
See http://docs.unity3d.com/ScriptReference/WSA.Tile.html

To remove your error put
using UnityEngine.WSA;
at the top of your script.

For tiled images look into sprites,
http://docs.unity3d.com/ScriptReference/Sprite.html