"Don't worry" "Don't worry about it" "Don't mention it" "No problem" "[It's] No biggie" (slang: "biggie" = "big thing") "[It's] No big deal" "[It's] No big one"

I usually say "no worries" when someone apologizes to me for something very minor. You can also say, "don't sweat it, bro!"

You'd say "no worries" in response to "thank you". Other options are: -You're welcome -No problem -Any time -(I'm) happy to help