I'm confused with 'Have' and 'Had'.

Have = eat.

I eat/have lunch before I go home.
I ate/had lunch before I came home.

Oh, no.... I have to tell a little story.

When I came home. My friend asked me that I already have food or not. He wants to make sure that I already done, so I want to tell him that I already ate it.

How can I say ?

My friends : Dude, Have you eaten yet. I have two sandwiches left?

Me : I have it OR I have had it OR I had had i

Hi,

A: Have you eaten (dinner) yet?
B: Yes, I've had it.

I had lunch already. Thanks.

mudclay I've had it.

Hi,
Normally, you say this to people who you have been putting with for a while. When your patience finally thinned out, you wil say " I've had it (up to here with you!)
To answer the lunch question, just say " I already ate".

When I came home my friend asked me if I had already eaten or not.

-- I have two sandwiches left. Have you eaten yet?
-- Yes. I've already eaten. OR Yes, I have.

CJ