Use "has been ___ing" to talk about something that started in the past, continued without stopping or happened again and again, and is still going on now:

You've been sitting there at your computer for over two hours.

I've been designing web pages for over ten years.

Or you can use it for a situation that you're not sure whether it's finished or it's going to continue:

It's been cloudy all morning, but it looks like the sun might come out soon.