Click "Config" and go to LED Preferences. This is where we'll set up the matrix size and physical configuration. 

If you have just one panel, set Chain Length to 1 and select the correct size of panel from the dropdown. Mine is 64x32.

Next go to Config / 2D Configuration. Select 2D Matrix from the dropdown and some options will appear. 

Enter the width and height of your matrix in the appropriate boxes and choose your orientation. You can come back and change this later if you end up hanging it in a different orientation.

Head back to the control screen. With 2D Matrix enabled, you'll see some new effects appear - you now have access to a dozen or so 2D effects. You can filter the effects column by clicking the box next to the little matrix (square) in the toolbar at the bottom of the effects panel.

Select one of the matrix effects and compare your matrix to the simulator at the top of the screen. If it looks the same, you've got everything set up correctly! Time to play.

If it doesn't look quite right, reset your board and repeat the last couple of steps, making sure you have your matrix set up correctly.