// your tile class that inherits a PathNode
public class MyTile : PathNode
{
    public MyTile()
    {
        // passible by default
        IsPassible = true;
    }
}

// creating a grid with size "width" and "height"
TileGrid<MyTile> grid = new TileGrid<MyTile>(width, height);

// make (0, 1) impassible
grid[0][1].IsPassible = false;

// starting point
Point start = new Point(0, 0);

// destination point
Point end = new Point(5, 5);

// points along the shortest path. The last flag is whether or not to allow diagonal movement.
List<Point> path = grid.FindPath(start, end, true);