Present Perfect Continuous

My clothes are covered in paint. I have been painting the fence.

In this case it does not matter whether something has been finished or not. We are more interested in the activity.

We also use the continuous tense to ask or say how long (for an activity that is still happening):

E.g. How long have you been reading that book?

Present Perfect Simple

The fence was grey. Now it is white. I have painted the fence.

In this case the important thing is that something has been finished. ‘Has painted’ is a complete action. We are interested in the result of the activity, not in the activity itself.

We also use the simple tense to ask or say how many times (for completed actions):

E.g. How many pages of that book have you read?