Foremost, you need user identification, be that logging in with a password form or just getting the user's Windows login name. If anyone can use the pc without logging in, then you need the db password type of identification. If not, you can research fOsUserName and see if that would be useful. Regardless, your db needs a user table. The easiest way to know who has logged in throughout a session is to open a hidden form that contains a field that contains their user id.
When they open the form to edit a record, you present a single record that is based on the fact that the record belongs to the user id value on the hidden form. If they are going to log out of the db and the db will remain open, you must close the hidden form and return things to the login screen. If they must close the db, you don't have to worry about closing the hidden form.
That's the basics of one approach.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.