Can you explain the difference between perfect and imperfect?

Question

...tenses that is.

Answer 1

Perfect means that an action is, was or will be complete at the time spoken of. "I went to Paris last year." "It will be finished by Christmas."
Imperfect means that the action was ongoing at the time spoken of. "I was travelling to Paris when...." I'm thinking about it." "I shall be studying it next term."

Answer 2

The perfect tense is used when action is perceived as completed in the past. The imperfect is used for continued or incomplete past action. Here's a visual image as an example: An artist painted a portrait. He looks at it and says to himself, "it's perfect." He never adds anything to it. So now, we say the "artist painted a portrait (perfect tense)." Another artist continues to work on his canvas, but keeps adding to it. He looks at it and says, "it needs more work, it's not perfect yet; it's imperfect." So now we say, "the artist was painting the portrait, or continued to paint the portrait (imperfect tense).
The imperfect is also used to describe an action that was happening before another completed action took place: "I was talking on the phone (imperfect), when my friend knocked (perfect) on the door." The first action is not perceived as completed while the 2nd action is.

Answer 3

Can someone tell me what is the right answer for this question?