@sonQ
Writting file is really easy.
If you want to hardcode filename, you can just use "Write File" action.
If you want to let user to choose filename, just add resource and use "Add Element" action from resources module. Check out this tutorials for more details
http://wiki.bablosoft.com/doku.php?id=how_to_let_user_to_choose_output_file_name
If you are writting account checker, I would recommend to use database, like @andy231 suggested.