하다 : Do or have some action ex) 자원봉사를 하다. Do volunteer work. 해요 : Let's do it. And It's relative honorific word between 해 and 하세요. 해 : An imperative sentence of do or morpheme of do in Korean. ex) 해볼까요? 해주세요. 해라. etc. 합니다 : It's best honorific word of 하다. I hope I'll be a help to you. :)

하- is the stem of 하다(to do), it doesn't make any sense by itself. 하다 is the basic form of the verb and this has no tense, therefore you'll find it only in the dictionary. 해요 = Do it. (kinda polite, informal) 해 is a casual way of saying "Do it", it's said between close friends. 합니다 is a formal way of saying "I do...".