The formal answer is '천만에요(chunmaneyo) It means your welcome.' But many Korean says just '네(ne)-it mean yes' and some times says '아뇨(anoy)- it means no, but this time it means no problem'

천만에요 is not really used. Check out this video for more detail: https://youtu.be/2RRKNE3Fjzo

You're welcome = 천만에요 (chun man e yo.)