There are certain verbs that go with "do" like doing homework, laundry, exercises (not exercise), chores, house work, the dishes, sports, shots (as in hard drinks like tequila)… These are phrases. "Did you do your back exercises today?", "Are you going to do the dishes?", "I do sports twice a week.", "We did shots last night and got drunk!", "I have to do my chores first." You eat or have soup and jelly, you take (or have in British English) a shower. When you use "did" with shower (as a verb), the way you used it, it's used for emphasis. For example, if someone said "you didn't take a shower" and you said "but I did shower".

you can use did only in past simple for question and with not for example did they go? (on past) they did not answer (on past) but, you can not say "they did answer" you can use for it ED or verb in 2 "they answed", "they went"

Ok Carce , I will try to explain to you As we study in ( Past Simple ) We use ( ed ) at the end of verbs that we use , and there are some exception ( or has special case ) For example : I studied English yesterday . The verb in this sentence is ( study ) , when we talk about the past We remove ( y ) and add ied . Ok , when I ask you Did you study yesterday ? You say : yes , I did ( you studied yesterday ) Watch this video to help you more : http://m.youtube.com/watch?v=YF2jRfFe82Y