Present Perfect Simple / Present Perfect Continuous

Present Perfect Simple

USE
- past action continues to the present
- completed past action still important in the present

IE
[+] He has visited his uncle
[-] He hasn't visited my his uncle
[?] Has he visited his uncle?

COMMON WORDS
- since, for
- already, yet, ever, just
- How long ... ?

Present Perfect Simple (2)

USE
- result of an action
- how many times an action happens
COMMON WORDS
- How many ... ?  ( result )

Present Perfect Continuous

USE
- process and duration of an action
- an action has either finished very recently or is incomplete
   (if you can see the effects of the recent action)

IE
[+] He has been writing a letter
[-] He hasn't been writing a letter
[?] Has he been writing a letter?

COMMON WORDS
- How long ... ?   ( action ) (hasta ahora, y todavía continúo)
- waiting for