Time expressions: perfect tenses

For and since

- We use for with a period of time (from the moment it started until now): They have been together for 23 years
- We use since with a point in time (the exact moment when something happened): They have been together since 1978

Been and gone

- Go has 2 past participles: been and gone.
                     We use been to mean 'go and come back': I have just been to the city centre
                     We use gone to mean 'go, but not back yet': She has just gone to the ciy centre

Adverbs and time phrases

- We use just to say something happened a short time ago. We don't use just  in negative sentences:
              We've just come back from the airport has happened

- We use yet to indicate that something hasn't happened
              I haven't finished it yet!

- We use already to say something happened sooner than expected:
            Mary has already arrived home.

More information here and here
More practice here