The expression “I’m good” is convenient, but not in the way you may think--not in its literal meaning. Informally, “I’m good” is a way to say “No, thank you” or “I’m fine” or “I don’t need it.”
If you’re an English learner visiting the USA, you may hear a conversation that goes like this:
Waitress/Waiter: Would you like some more coffee?
Customer: I’m good (meaning “No, thank you”).
OR
Do you need any help carrying those bags?
No, I’m good (meaning “I don’t need any help”).
This is a typical example of the idiomatic way we often speak and using “I’m good” will show that you know American English rather well.