In LotusScript you have the Send method in the NotesDocument object.
Given that you mention Submit, I'm guessing you want the document to be mailed from a Web client. You can do this by adding LScript to the PostSave event, where it checks that all fields are properly filled in and then mails the document.
Beware though ; if you do not pay attention in your code, the doc will be mailed every time it is saved - this might become an issue if you don't put in the proper check to prevent that.
Pascal.