헐 means damn! 어머 means shit! It is just a my opinion. haha

감사합니다!

헐, 어머, 대박 and so on.. they are all expressions for someone's emotions, usually when you are shocked or surprised. Similar to "OMG/ what?!/ Oh, no./ WTH...." For example, when you are asked to do all the house chores in a day, you can say; "헐~~" When someone throws a ball at you without a notice, you can say "어머!" I think you may get chances to hear them in many contexts. Don't try to perfectly practice the phrases because they are kind of slang and for young people.