Difference between I had Written and I have written

Hi,

Please let me know the difference between "I had written" and "I have written".
For example :

I already completed some work then I should use I had written for the same thing I can use I have written also then what is the difference between both of them.

Regards,
Ray.

Hi Ray,
Welcome to the forums.

Past: I wrote something. I wrote it yesterday. Completed action, in the past.
Present perfect: I have written something I want you to read. The action is complete, but it connects to the present.
Past perfect. I had written something and shared it with a friend, and then I saw my writing with my friend listed as the author. I felt completely betrayed. -- Use this for a completed event in the past that comes before something else also in the past.

thanks alot it helps.