You don't "create" multi users -- Access is multi-user enabled right out of
the box.

You can improve multi-user reliability and performance.  My first suggestion
is always this: "Split the front end (queries, forms, reports, macros, and
modules) from the back end (tables, relationships, and data). Give each user
a copy of the front-end database, linked to the tables in the back end,
which is stored in a shared folder on a machine in the LAN.  You can use the
Linked Table Manager, or write your own code, to link the tables."

Then I advise visiting MVP Tony Toews' site
http://www.granite.ab.ca/accsmstr.htm, for other good tips and hints on
avoiding corruption and performance.

There are some situations in which you want "protection", in which case I
advise going to the Knowledge Base at http://support.microsoft.com and
searching for Security FAQ for Access.  It's 30 pages with no filler at all,
so read it carefully.  Alternatively, if you are just trying to identify
who's making updates, you can see the API section at
http://www.mvps.org/access and retrieve a windows logon name.  If you are
developing in Access 2007 ACCDB, the Access workgroup or user-level security
is not supported and you'll have to "roll your own" security.

Larry Linson
Microsoft Office Access MVP