past continuous tense用法

Past continuous tense

We use the past continuous tense to talk about an action that continued for a period of tome in the past.
We often use it to show that the action began before a particular time in the past and continued after it.

We also use the past continuous tense to talk about what was happening when another action took place.
We use the past continuous tense for the longer action and the simple past tense for the shorter action.

for example, While i was watching the TV, the phone was rang.

while is for the longer action
when is for the shorter action

P.S: some of them are copied from my 2B Longman express textbook
some of them are my opinions.

Past continous tense means what you are doing in the past.
You would use past continous tense on :

e.g. He knocked the door while I was watching TV.

In this situation, '' was watching '' is a past continuos tense, and ''knocked'' is past tense.

In conclution, you would use past continuos tense when it is a long action which was doing in the past.