Just is used always with the present perfect to refer to an action which has been done very recently (what in Spanish we say with the expression ‘acabo de..’) JUST always goes after have or has and before the main verb.
I’ve just seen Tom in his car Sarah has just arrived We have just finished the exam
Alreadymeans that something happened earlier than we expected. With Present Perfect already usually goes after have or has and before the main verb. Examples
- We've already had our breakfast.
- When are you going to do your homework?
- But I've already done it!
- Do you want a cup of coffee?
- No, thanks. I've already had one."
Yetmeans that something that we expected has happened or hasn't happened. We usually put it at the end of a sentence. Examples
- Has the post arrived yet?
- Have you done your homework?
- Not yet.
- Haven't you got ready yet? Look at the time!
FOR FURTHER PRACTICE on already, yet & just CLICK HERE