“Do” and “does” are both helping verbs, and they are used in present simple tense. The difference is based on the subject. Use “do” with I, you, we, they: I do my homework. You do a good job. We do exercise daily. They do their work. Use “does” with he, she, it: He does his homework. She does well in school. It does not work properly. In questions: Do you like coffee? Do they live here? Does he like coffee? Does she live here? In negatives: I do not (don’t) know. He does not (doesn’t) know. Simple way to remember: “Do” is for plural and I/you/we/they. “Does” is for singular third person he/she/it.