When the object of a sentence is a person, we mark the object with i or ki:
Kei te kōrero ahau ki te wahine.
I am talking to the woman.
Or:
I kite ahau i te kaiako.
I saw the teacher.
However, if the object of the sentence is a personal pronoun - me, him, her, us, them, you - then we have to put an a in front.
For example:
Kei te kōrero ahau ki a koe.
I am talking to you.I kite ahau i a rātou.
I saw them.
This also true of the word for he and she - ia - except that i a ia is pronounced "ee eye a":
Kei te kōrero ahau ki a ia (ki-eye-a).
I am talking to him or her.
It's always tricky when we encounter a word or an idea that has no equivalent in English. People striggle with concepts like i and ki or the a and o categories because we don't have these concepts in English.
One similar thing is the use of a in Māori as a personal article. There is no equivalent in English.
Before a person's name, in most sentences, we put the word a before a person's name. This happens when the person is the subject of the sentence:
Kei te waiata a Mere.
Mary is singing.Kei te kōrero a Hemi.
Hemi is talking.
We also use the a before a person's name when they are the the object of the sentence:
Kei te kōrero ahau ki a Rangi.
I am talking to Rangi.Kei te waiata te wahine ki a Mere.
The woman is singing to Mary.
All of the personal pronouns take a when they are the object of a sentence:
a au
a koe
a ia
a rātou
a koutou
a tātou
etc
But there is one exception - we do not need the a before ahau.
So we would say:
Kei te kōrero te wahine ki a au.
The woman is talking to me.
But:
Kei te kōrero te wahine ki ahau.
The woman is talking to me.
Not "ki a ahau".
When a pronoun (except ahau) follows any of the particles kei, i, ki, hei it takes the personal article a:
Kei a Pita te hokomaha.
Peter is at the supermarket.