I'm wanting to create a manga to send into publisher, what are the necessary things I should do

I do not think u will find any help in the Writer is Market. I've checked in the past.but I could be blind.

Graphic novels work a little differently than publishing a novel. For one thing, u do not necessarily need an agent. Tokyopop accepts all kind of submissions, but u have to follow their guidelines (they're listed).

http://tokyopop.com/Submissions/gopro/286656.html

Dark Horse comics still accepts unsolicited submissions, but they wo not mail u back ur documents (so do not send original art.)

http://darkhorse.com/Company/Submissions

Del Ray seems lax with their submission guidelines:

http://randomhouse.com/delrey/manga/submissions.html

Oh yeah, post manga/art questions in Drawing & Illustration next time, including publishing questions. Some of those guys know a bit more about this than I do.

Check Writer is Market at the public library to see if they have any manga markets. You might be interested in the link below as well.