For example if i wish to make registration in form element can i give action any name? For example < form action = “/submit-user” > can i use it like this?
Not really, it refers to where you send the form to, so it’s constrained by the URI/URL/etc for that service/resource/etc. If you control that (like you have say a PHP file that does it) you can call that resource anything you like and the action attribute would be the same.
If there are some special rules, like the action is only a placeholder and everything gets handled by something else then sure
you can always give the form an id