Example: You have Medicine skill 3 (like a med-school intern after a few months of practice) and an Intelligence of 4 (above-average), you'd roll 4d10 at difficulty 7 to diagnose a disease.You roll a 2, a 6, an 8, and a 9 -- two successes, and you've got a pretty good diagnosis.
Example (continued from above): Your GM is rolling 2 Magic dice, with a Curse number of 2. He rolls a 16 and a 1. That means you get a Charm (the 16 matches the 6 on your regular dice) and also a Curse (the 1). Your GM rules that with your Charm, you notice the signs that your friend's illness may be the result of malevolent spirits, and with the Curse, that you've opened yourself up to the same malevolent spirits.