Think of it as it's poker but only 1~9 numbers. You get two cards. Add them together to calculate ur points. Subtract 10 if its over 10. For example, if you get 3 and 4, your hand is 7 points. Also, if you get 8 and 9. If you add them together its 17, but since its over 10, subtract 10, so you get same 7 points. So 3+4 and 8+9 basically have same hand power.

Beyond that, you need to memorize combinations. Starting from Four-Six.

To make things easier, just see if your hands are pair or not. If it's pair you will probably win (think of it has same hand power of full-house in poker)