This is used to describe a continuous or repeated action that's still happening. The action can be something that happens continuously:
They've been arguing with each other.
Or it can be an action that is repeated over and over for a length of time:
I've been going to that grocery store for over 25 years.
You can tell long the action has been going on using "for (how long":
The beans have been boiling for about 10 minutes.
Sometimes "for" can be dropped, like in the example at top, in spoken English in casual settings.