Did points to finished time: I did the dishes last night. Do points to now or habit: I do the dishes every evening. Add a time word to your sentence, then match the form to it.
The pair shows the shift: Did you call him? asks about yesterday. Do you call him? asks whether that is your habit. Same words, different times.
Paired examples
I did my homework in record time. The speaker looks back at one finished event. I do my homework every evening. Here the routine still happens now.
They did the accounts this morning. The task is complete. They do the accounts on Fridays. That describes an ongoing schedule. Same activity, different time viewpoint.
Some sentences allow either form, with the meaning shifting. I did the dishes after dinner reports one finished occasion, while I do the dishes after dinner presents a regular habit. Both are grammatical; did looks back at a single completed event, do signals a routine that still applies.
One caveat worth knowing
Some sentences carry no time signal at all. I do my best. She did her best. Without yesterday or every day, the choice rests on viewpoint alone. Ask whether you are standing inside the moment or looking back at it, and let that answer pick the form.
Watch for hidden time in the surrounding sentences. If the paragraph already says last month or back then, did fits even in a bare clause; if the frame is now or usually, do does. Both forms work with any subject, so the surrounding time words decide.