Past progressive: I was watching TV.
This means that at some point in the past, I was sitting in front of the TV, watching it.
This is just like the present progressive, except that present progressive indicates an action now, and the past progressive indicates an action then.
Do not disturb me: I am having a bath now.
When you knocked on the door, I was having a bath.
Present perfect progressive: I have been living here for eight years.
This means that eight years ago, I started living here, and I am still living here now.
The present perfect progressive indicates an action that began in the past and continues into the present.
So, the past progressive is for actions that stopped in the past, and the present perfect progressive is for actions that didn't stop in the past.
These examples are a bit more confusing:
I have been watching that new TV show. (There is an episode every week. I watched an episode in the past, liked it, and watched the next episode, then the next, and so on. I intend to watch next week's episode.)
I was watching that new TV show. (But you switched off the TV, so now I am looking at a blank screen.)
Julie: Hey, Dave -- you missed our date. We were supposed to meet at 8 o'clock. Where were you?
Dave: I was waiting for you, at the cinema. But you didn't come, so after an hour I went home again.
Julie: But we arranged to meet at the theatre. I was waiting for you there!
Pete: Ah, there you are!
Rose: Sorry I'm late. Have you been waiting long?
Pete: No, only ten minutes.
In the first scene, Dave stopped waiting and went home again. In the second scene, Pete didn't stop waiting until Rose arrived.