error in creating mesh script

Failed setting triangles. Some indices are referencing out of bounds vertices. is the error im new to creating meshes but i think the problem is the variables on the top i dont know what to put in them, i want to create a plane do i put 3 vertices and 2 triangles ?? and whats do i do for xyz

 var newVertices : Vector3[];

var newUV : Vector2[]; var newTriangles : int[];

function Start () { var mesh : Mesh = new Mesh (); GetComponent(MeshFilter).mesh = mesh;

 mesh.vertices = newVertices;
 mesh.uv = newUV;
 mesh.triangles = newTriangles;

}