my own theme and categories in backend

Hello,

I just start to use WP. I have tried to find some informations in google but with no luck.

I’ creating my own theme. I have created back-end site to create my posts and almost everything works good. Almost, because I need to bins my post with category and don’t know how to add categories box to editing site. In default ‘add new’ category box is on right column…

Please help me.