I had the same question when I was sttnriag. But i reserched and now I have improved. If you want to write manga first create a storyboard. There are different types. I prefer narrative storyboard they allow me more creativity. However you may prefer panneld story boards. Also learn the various types and techniques. There is a great mangaka named Mark Crilley who does videos on youtube. I will put a link to his channel in the sources along with some shops to buy supplies and tutorial web sites. For supplies you should use what you feel comfortable with. However for a basic supply list i can tell you some. B4 manga paper, screentone, black ink (sumi ink, india ink or drafting ink your pick), white ink, nibs,nib holders, g pen nibs,copic markers, triangles, templates, feather sweeper, rulers, x acto knife, brushes, pencil set (prefferably 9b-9h). There are more supplies but this list should get your started. However if you can not afford it use what you have around.You also should pour through books,tutorials, learn techniquesfor drawing etc and watch a mangaka draw. Even if you have to do it through a video on youtube. Watch how they draw manga and read manga and watch anime as well. This is crucial. I would also suggjest keeping abook of all the manga terms you have learned fo you can look back if you forget as well as an idea book. Also contact mangaka. you can do this by writing a letter to the publishing company they are attached to asking them to forward your letter. Although Mangaka are busy so I can't promise they will always respond but, they will see your letter. I also should mention that you can go into the manga field simply as a manga writer. Either the publishing company or yourself will end up pairing you with an artist. But if you want o go into the manga field. Ask your self if you truley want to. If you do stop at noting to achieve your dream. You must make manga your life to succeed in it. I hope this helps. Check out the links in the sources.