Perfect Continuous tenses in the active voice

Present Perfect Continuous
Subject + have been + Ving
The present perfect continuous tense is often used (with for or since) to describe how long something has been happening up to now.
For example:- How long have you been studying English?" -I've been studying English for four years."
-How long have you been living in Germany? -I've been living here since 1998.

The present perfect continuous is also used to refer to an event that may or may not be finished when it's effect can be seen now.
For example:- Look! It's been snowing.
You should also use the present perfect continuous when talking about how long you have been doing your current job or working on unfinished projects:
For example:-I have been working at BT for three years.
We have been exporting to China since 1999.

Past Perfect Continuous
Subject + had been + Ving

The past perfect continuous tense is used to talk about longer situations that continued up to the moment in the past we are talking about.
For example: "By the time I left England we had been living in Bristol for five years."
"Her back was sore because she had been sitting at the computer all day.“
It is also used to say how long something went on for, up to a time in the past.
For example: We apologised because we had kept them waiting for 3 hours.
We apologized because we had kept them waiting since lunchtime.