How do I post manga onto the website?

Hmm...hard to answer. First you should check out if it's licensed in English or not and whether it's a Libre publisher manga or not. Scanlating & distributing mangas itself is illegal. But the aforementioned 2 are the landmines. So you should not do it if it's licensed or a libre title.
Next, if you are clear of the landmines, you should ask the group/owner whoever published the scans for their permission to re-translate it. And if they give you permission then, go ahead, translate it, if possible share it with us (≧∀≦)
PS. If it's licensed or libre title, you can still translate it for fun. But you have to be very careful later as to whom you share it with (for eg. sharing it with only friends whom you trust.....not everyone)

IM BACK! I asked the scanlations if I could translate the manga. It's been 20 minutes since so. I'm not sure if they would really "understand" my really bad Vietnamese. Well, I hope they reply soon and everyone could read it! I also checked if it's licensed. There hasn't been anything that says that it's licensed. I'll update as soon as possible. :)

Great!! Hope you get the scanlating team's permission soon! A huge thanks to them and you in advance, as Natsume Isaku is 1 of my fav mangakas. So i am looking forward to it ヾ(☆▽☆)

Go to any manga page (I prefer relevant mangaka or manga), Click on the little flag on the left screen edge to contact admin to upload for you.

You also can ask admin about all those questions.

Lol tbh isnt this site already considered "illegal"? We're basically taking all these things that are meant to be paid for and thwn just distributing it so why even bother asking if its legal anymore hah

Sorry, I'm new to this stuff.