The present perfect continuous is used to express how long a current activity has been going on. It is often used in context to provide a reason for a present result. Remember that continuous forms can only be used with action verbs.
This tense is often used with the following time expressions:
since + specific point in time
for + amount of time
Subject + has / have + been + verb + ing + object(s) + time expression
He's been cleaning house for two hours.
Subject + has / have not (hasn't / haven't) + been + verb + ing + object(s) + time expression
Janice hasn't been studying for too long.
(Question Word) + has / have + subject + been + verb + ing + object(s) + (time expression)
How long have you been working in the garden?