When do you use it?  -> pg 89 in your textbook
- When something started in the past, and is still happening now. 
- When you want to emphasize that something has been happening for a long time, or to emphasize that something has not finished yet. 
-When something has happened for a vague amount of time. 
I have been studying English for six years.
He has been sleeping since the start of the lesson. 
She has been writing all weekend. 
They have been talking all day long.