Site forms — contact, request, signup — are built here, and their submissions land here.
Submissions are always stored
Every successful submission is recorded in this module, whatever else you have configured.
So if a notification email did not arrive, the submission is not lost; it is in that form's submissions list.
What happens afterwards is additional
Besides storing, a form can send an email, create a lead, or post the data to an external address. These are layered on top of storage, not instead of it.
If one of them fails the visitor's submission still succeeds — otherwise an external failure would be shown to someone who can do nothing about it.
Forms are built in the page editor
Forms are laid out with the same tool as pages. Layout, wording and field order are free to change, and what you see in the editor is what the visitor sees.
Validation is re-run on the server. Editing the form in a browser does not change what the server accepts.
Changing a form does not change past submissions
Deleting or renaming a field does not rewrite submissions already recorded. They stay exactly as they were sent.