What is the difference between the meanings of the perfect and imperfect tenses?

The perfect and imperfect tenses in latin are both used to describe actions which take place in the past, but they are used to describe slightly different types of actions.
The perfect is used to describe actions that have been completed, or happen entirely in the past. You can translate the perfect in a few ways but the most common are 'I arrived' or 'I have arrived'. In English sometimes you can use 'did' to translate the perfect too e.g. 'I did arrive early'.
The imperfect on the other hand describes actions which had no particular start or end point, or have not been completed. The imperfect often translates to English 'I was arriving' or 'I used to arrive' but sometimes its best to translate it with the simple past 'I arrived'.