Sooo

go to any pre-existing manga, click on the flag to the left and there should be an option to upload a new manga

I hope this helps (●'◡'●)ﾉ
http://www.mangago.me/home/photo/5318652/

Note: click on the zoom button to make the image clearer :)

Oof wrong link, here it is :>
http://www.mangago.me/home/photo/12388126/

lowkey promoting my work lol. here ya go :">
http://www.mangago.me/read-manga/mangago_how_to_guide/