1. 못 means 'can not'. e.g. 저는 우유를 못 마셔요. ( I cannot drink milk.) 저는 운전을 못 해요. (I cannot drive.) 2. 전혀 means 'not at all'. e.g. 저는 전혀 안 피곤해요. (I am not tired at all.) 저는 전혀 안 바빠요. (I am not busy at all.) 3. 절대 means 'absolutely, completely' or 'never'. e.g. 물은 우리에게 절대 필요하다. (Water is absolutely necessary to us.) 군인은 대장의 명령에 절대 따라야 한다. (Soldiers absolutely have to follow the commander's order.) 이 말은 절대 다른 사람들한테 하지 마세요. (Never tell this to other people.)

Going into more details, 절대 (absolutely) is probably the closest of the three to "never". (Note that 절대 is a rather colloquial version of the better sounding 절대로.) - 그런 일은 절대(로) 안 일어나요 = That kind of things absolutely don't/won't happen = That kind of things never happen. - 이건 절대(로) 만지면 안 돼요 = You should never touch this. 전혀 is "(not) at all' as was mentioned, which can mean "never" in certain contexts. - 그런 일은 전혀 없어요 = That doesn't happen at all = That never happens. 못 is more subtle. It normally means "be unable (to do something)" but there is a usage (advanced kind) that can be translated as "will not" or "will never", i.e. a strong refusal to do something. This sounds confrontational, so it's not used in normal everyday situation. - 무슨 말을 하셔도 그렇게는 못 해요 = No matter what you say, I won't/will never do that. Also note that "never" referring to past experiences is not expressed using any of these words. You need a phrase like "-(은) 적이 없다" for that. - 저는 (한 번도) 뱀을 가까이에서 본 적이 없어요 = I have never (even once) looked at a snake up close. In short, there is no single phrase that corresponds exactly to "ever" or "never".