Hello Zahra! I'm a native-speaker born in Russia, but living in South Africa. I like your question and I like English tenses. They seem complicated until you figure out the logic behind it. Then it becomes clear.
So as for Present Perfect Continuous shows that something started in the past and has continued up until now. You don't have to mention the duration of the activity, but there often is an indication of the moment when it started.
<em>It has been raining since Tuesday.</em> - no duration indicated, but we know that since Tuesday and up until now the weather has been rainy. 'Since Tuesday" is an indication when it started.
<em>What have you been doing? - I have been cooking.</em> - again, no indication of duration. But we know that up until right now the person has been cooking for a certain length of time. The activity started in the past and is still going on or just finished.