English has a few different tenses when you want to speak about an event in the past, and these are designed to cover the differences in these events. The following sentences are examples of these different conditions:
I used to sell flowers.
I sold flowers yesterday.
I was selling flowers when you called yesterday.
I have been selling flowers for 1 hour.
I have sold 5 flowers.
I had been selling flowers for 1 hour when you called.
I had sold 5 flowers when you called.
Before we look at these sentences in detail, there are some things we need to be clear on.
The past deals with two ways of looking at time: FINISHED TIME and OPEN TIME.
If an event happened yesterday, then it is over, and that is finished time.
If an event happened today, a few hours ago, but today, and today is now, then this time includes the past but is not finished. This is open time. This year, in September, is open time, so an event that happened in January, which is this year, is open time.
Another thing, if the time is not specified in a sentence, you have to assume it's open time. For the sentence to use finished time, it has to say it specifically. Let me give you an example:
I sold flowers yesterday. - yesterday is finished time.
I have sold 5 flowers today. - today is open time.
I have sold 5 flowers. - as the time is not given, it is open time.
The second thing we need to look at is whether we are interested in the event, the specific time the event happened, or the duration of the event. Each one of these changes which verb we use. For example:
I sold flowers yesterday. - just the event.
I was selling flowers WHEN you called yesterday. - specific time.
I have been selling flowers FOR 1 hour. - open time and duration.
Now that that is clear, we can look at the different ways of using the past. There are several different verb tenses we can use:
Present perfect continuous
Present Perfect simple
Past perfect simple
Past perfect simple
The past simple is used for describing just an event in finished time. It gives no information about specific time or duration:
I sold flowers yesterday. (past simple)
The past continuous is used for describing the specific time an event in the past happened, but it doesn't give the duration:
I was selling flowers when you called yesterday. (past continuous = finished time and specific time: when)
The past perfect continuous is used for describing the duration of an event in the past:
I had been selling flowers for 1 hour when you called yesterday. ( past perfect continuous = finished time, duration)
The present perfect continuous is used for describing the duration of an event in open time:
I have been selling flowers for 1 hour. ( present perfect = open time and duration.)
There is a special case of the past simple for events that we did in the past and no longer do:
I used to sell flowers. (used to = finished time, no longer happens, no specific time, and no duration.)
When you do an activitity for a duration of time, there is usually a result of this activity:
I have sold 5 flowers BECAUSE I have been selling flowers for 1 hour.
I have sold 5 flowers. (present perfect simple = open time, and result of present perfect continuous.)
I had sold 5 flowers when you called yesterday. (past perfect simple = finished time, and result of past perfect continuous.)
There are a few things of things left to mention:
Whenever you use open time, you must use HAVE.
HAD is used to put one event in the past before another:
When I arrived, they left. ( at the same time)
When I arrived, they HAD left. (before I arrived.)
The continuous tenses are used to define a SPECIFIC TIME:
I was selling flowers at 8 p.m. (past continuous - spefic time)
I am selling flowers now. (present continuous - specific time)
I will be selling flowers at 8 p.m. tomorrow. (future continuous - specific time)