We use Present Simple Past Simple Present Perfect :

• for a finished action which has an effect or result in the past present future :

  I have sliced a cucumber. Let's put it in the salad;

• with such time adverbials as just, already, yet:

  She's already done her homework;

• for an action that started in the past present future and is continuing into the past present future :

  My grandma has lived in London since her birth. Her flat is in Hampstead;

• to talk about our experience in the past present future without specifying the time:

  We've seen this film before. Let's choose another one.

The short form of "I have" is "I've" "I'eve" "I'd" .

The short form of "she has" is "she'as" "she's" "she'es" .