Theory:

Use of have/has in Present Perfect Negative sentences:
 
S + have/has +not+ V3 + O
 
S - subject: I, we, you, they, he, she, it, Mary, John…
V3 - the Past Participle of the verb (the verb in the third form): written, eaten, worked...
O - object
  
S
have/has
not
V3
O
I
have
not
eaten
two apples
We
have
not
eaten
two apples
You
have
not
eaten
two apples
They
have
not
eaten
two apples
He
has
not
eaten
two apples
She
has
not
eaten
two apples
It
has
not
eaten
two apples
 
Important!
Short forms:
 
have not = haven't

I have not eaten = I haven't eaten

has not= hasn't
She has not eaten = She hasn't eaten