I have been married for 46 years. (I am still married, but I'm looking back at all those years I have been married). This is the present perfect tense. I had been married until I got a divorce, and now I'm no longer married. This is the past perfect tense.

If you are continuing an activity that you were doing, you might choose to say; "I have been doing this for some time. I have been doing it for at least 3 years. I have been doing it each Saturday during these years." We know these years are the last three years because they are still going on now. It tells us you have not stopped. If you quit at some point and you do not do it anymore- Use had been. "I had been doing this for some time. I had been doing it for at least 3 years. I had been doing it each Saturday during those years." We do not know when those years were, but we know they are over. This lets us know you were doing it regularly, but not anymore.