I am always confused about when to use "I did something..." and when to use "I have done something..."
Please kindly explain and provide some examples.
"I did" is the "simple past" form.We use the Simple Past to express the idea that an action started and finished at a specific time in the past. Sometimes, the speaker may not actually mention the specific time, but they do have one specific time in mind.
I saw a movie yesterday.
I didn't see a play yesterday.
Last year, I traveled to Japan.
Last year, I didn't travel to Korea.
Did you have dinner last night?
She washed her car.
He didn't wash his car
Have done is the "present perfect" form. Basically,when we use the Present Perfect it means that something has happened at some point in our lives before now. Remember, the exact time the action happened is not important.
I think I have seen that movie before.(unspecified time)
I saw that movie last week.
We often use the Present Perfect to list the accomplishments of individuals and humanity. You cannot mention a specific time.
Man has walked on the Moon.
Our son has learned how to read.
Doctors have cured many deadly diseases.
Scientists have split the atom.
There's a lot more to it; follow the links for a more thorough explanation.