When speaking English as a second language, it’s often difficult to decide how to answer a question.
Begin by thinking about “when”, or the time frame which the sentence is referring to.
The easy way to do this is to look at the tense of the question–like this:
A: What did you do today?
B: I bought socks.
The questioner using the helping verb did, which tells us the question is about the past, so the answer should be in the past, too. Thus the answerer uses the simple past form of buy.
Here, a girl and her father are in a restaurant. The girl is watching a waiter and asks about her.
Daughter: What is she doing–the waiter?
The girl is asking about what’s happening now.
Father: She taking the man’s order.
So the father answers in the same style–the tense of the daughter’s question….
Daughter: That’s her job?
So the father answers in the that same tense:
Father: Yes it is–and bringing the food.
Now the daughter switches to the present Simple–asking about usual activity:
Daughter: She takes order and brings food all the time?
Daughter: What‘s she doing now?
Father: She‘s going to the kitchen, now.