Let me try to explain better. The cards have a power value (the number on the top left corner). Right next to this value there is a note, that can be either simple (♪), double (🎵) or triple (there is no Unicode symbol for that sorry). This means that the points you get from the card will be applied once, twice or three times respectively. So if you have a card with 3🎵 in the top-left corner, you'll get 3 x 2 = 6 points.
Now let's talk about the top-right corner. In this corner you have a bonus that will be applied to the next card in line. Let's say we place the 3🎵 card to the right of a card with a +2 bonus. Now our 3🎵 card becomes a 5🎵, so you'll get 5 x 2 = 10 points. The bonus can be negative though, or even a multiplicator. So if you apply a bonus of x-1 to you 3🎵 card, it becomes -3🎵, so you'll get -3 x 2 = -6 points.
So the optimal strategy is to try to give the biggest bonus to the best suited card. A +2 is better on a triple note, while a x3 is better on a +4♪ than a 1 triple (3 x 4 x 1 > 3 x 1 x 3). You also have to manage the negative bonuses, to avoid losing points (you'll lose less point applying a -4 on a simple note than a triple for example).
The color is only there to differentiate the cards. Once you know them you'll only need to see the color to know which card it is (the pink one is a 0 triple, x-1 bonus for example, while the blue one is +4♪, +2.)
I dont know if my explanation made it better or worse, but anyway thanks for playing!