How to create a new long text?

Hallo guys, I am creating a single screen aplication. After pressing a button I have to create a long text do the document which I am creating. How to do this?

I have tried FM 'CREATE_TEXT' but I dont know which values have to be passed into this FM. What is fid, fname and fobject? I have created also a long text objects for order header but how to use it? Thank you