They're often used idiomatically so it'd be better not to worry too much. However, "opportunity" is a little more specific and tangible: "I have an opportunity to study abroad next year." = "It's a definite possibility that I will study abroad next year, as long as I work hard." Chance, on the other hand, is a little more unsure/ambiguous. "You have a chance to win the basketball game tonight." = "You may lose the game and you may win the game. But it's AT LEAST possible that you will win the game." However, as I said, there are idiomatic uses. An often used one in English is "take your chances" which means "you don't know if you're going to succeed but just try. Who knows what will happen." For example: "I want to talk to that girl, but she's so pretty. I'll be too nervous." "What's the worst that could happen, she rejects you? Take your chance! Go talk to her."

"Chance" is more often used with something involving luck and less certain. Example - "Why take a chance if you don't need to?" People use "opportunity" to describe things that have more likely good possible results. "That's a good business opportunity. You don't want to miss it."