____
|  1  |
|2 3 |
|_4_|___
|      |  2  |
|      |3 4 |
|___|_5_|

Now, you see the blank space?

____
|  1  |
|2 3 |
|_4_|___
|  1  |  2  |
|5 2 |3 4 |
|_3_|_5_|

The card that was inserted into the black space now interacts with the other two. The top number of the inserted card + teh bottom number of the top card = the right number of the inserted card + the left number of teh card on the right.

In other words:

4 + 1 = 5
3 + 2 = 5
4 + 1 = 3 + 2

Since the connecting parts add up, it then turns the two cards.

_______
|  1  |  5  |
|2 3 |A 4 |
|_4_|_1_|
|  1  |  2  |
|5 2 |3 4 |
|_3_|_5_|

Now, the same situation, but the important part to notice is the top-right card. IF you take the top-left and bottom-right cards via the plus rule (or the same rule when it comes down to it), you can then possibly combo into the top-right card. This is done by comparing the numbers on the turned card to those they touch on the top-right card. So:

3 < A, therefore it cannot be combo'd that way.
2 > 1, therefore the card can be combo'd.

If the number on the turned card is higher than that of the card it touches, it then combo's that and flips. The combo then carries on until it reaches a point where either all of the cards have been turned over or it can't turn over any more.

I hope that all makes sense =P