Continuous Form: Advanced Uses

Repeated
We use the continuous form for repeated actions, actions which happen again and again.
The door was banging because of the wind. It woke me up.
The door did not bang only one time: it banged many times.

We use the continuous form this way especially for short actions.

Length of Time
We often use the continuous form when we talk about a length of time. We can use a simple form instead of a continuous form there, but the continuous makes the verb stronger. It tells the listener that the time is unusually short or long.
She was waiting for three hours, but the phone did not ring.
I am working here for two months.
The ice cream will be sitting in the car for forty minutes. It will melt.

Important
We use the continuous form to make a verb stronger, and so we use it when the verb is especially important. This is most common in complaints and excuses.
You are always doing that! It makes me furious!
I didn’t do anything! I was just sitting here!

Infinitive
We use the continuous infinitive form, (to+) be + present participle with (modal) or other (auxiliary) verbs as the finite form.
You are too tired. You should be sitting now.
I like to be doing something all the time so that I don’t get bored.

We use the continuous infinitive when we want to use a modal verb for an activity around a time.
He has not answered his phone. He might be working now.
The baby may be sleeping when you come home tonight, so be quiet.

Combination
We use the continuous form with the perfect form to make the verb stronger. Sometimes, the action is finished, but this is not always true.
I have broken my foot. (one complete action before now)
He has been breaking bones all year. (repeated actions before now)

I have tidied the house. (The house is now tidy.)
I have been tidying the house. (It was hard work; I am tired; you do not know whether the house is now tidy.)

We use the continuous form with the (passive form) if the verb affects the subject.
Tennis is being played on three of the courts, and basketball on the fourth.
The door was being banged against the house.