Well, Access in a multiuser environment is not exactly an "elementary level
subject" but I will try to not make it overly complex.

Having multiple users logged in to the same front-end database or monolithic
database significantly increases the chances of database corruption. An
appropriate configuration is that each user has a copy of the front-end
(queries, forms, reports, macros, and modules), linked to tables in the
shared back-end (tables and data). You make your changes on your
"development" copy of the front-end, and distribute it to the users.

You'll find some of my thoughts on Access in a Multiuser Environment, at the
introductory level, posted at http://appdevissues.tripod.com/downloads.htm.
The most comprehensive collection of information and links on the subject
that I know about is at MVP Tony Toews' site,
http://www.granite.ab.ca/accsmstr.html.

The simplest way to "force users out" is to include in the front-end's
opening form a timer that periodically checks data in the back-end (set only
by the administrator, in this case you), warns the users, and then quits
after they have had time to save work in progress.

Best of luck with your project.

Larry Linson
Microsoft Access MVP