JUST, YET, ALREADY, EVER, NEVER, FOR, SINCE

These words give us a clue that the tense we must use is the Present Perfect (though they can be used with other Perfect tenses) because they are related to the present moment. However, it's not always clear when it come to usage. Here's a brief explanation (with translation for speakers of Spanish) on how and when to use each one.

JUST- "acabar de". 

• It means that something happened a very short time ago.
  

He has just started a new job (Acaba de empezar un trabajo nuevo)

The film has just started (La película acaba de empezar)

YET- "aún no/todavía no/ya"

• It's used in negatives and questions at th end of the sentence
  

I haven't finished yet (Todavía no he terminado)

Have you finished yet? (¿Ya has acabado?) it means : I don't know if you have finished and that's why I'm asking

ALREADY: "ya"

• It is used is affirmatives and questions.

I have already started (Ya he empezado)

Have you already finished?(¿Ya has acabado?) It means: I know you have finished and that was quick. You have finished before expected

 

EVER: "alguna vez"

• It is used in questions with the structure "Have you ever+past participle...?

Have you ever been to Japan? (Has estado alguna vez en Japón?)

 

NEVER:"nunca"

• It is used with the present perfect and placed after the auxiliary "have/has"
  

I have never been to Japan (Nunca ha estado en Japón)

He has never studied German (Nuca ha estudiado alemán)

 

FOR: "desde hace"

• It is used to talk about something that has happened over a period of time

He has lived here for 15 years (Ha vivido aquí desde hace 15 años)

It can also be translated as "Lleva viviendo aquí desde hace 15 años" o "Vive aquí desde hace 15 años" but be careful: "He lives here for 15 years" is wrong in English 

 

SINCE: "desde" o "desde que"

• It is used to express the point of time at which something started and which applies to the present time

He has lived here since 2005 ("Ha vivido aquí desde 2005" or "vive aquí desde 2005) but be careful: "He lives here since 2005" is wrong in English