You can use edit or firetxt commands to create new files or to edit an existing file. Both edit and firetxt refers to the same command and thus they both have the same syntax as follows:
edit [<filepath>]
Here the "filepath" is the path of the file you want to edit. If the specified file does not exist, the file is created. Edit or firetxt commands actually opens the FireTXT text editor in a new tab.
If you don't specify the "filepath" then FireTXT is opened in new tab with the title "untitled".