If by "working on it" you mean making changes to the design, you can't. With
some very old versions of Access you could, but not any more.
That leaves three possibilities:
1. Come into work late at night and on weekends when no one else is using
it. Don't laugh. I worked on New Years Day for that reason.
2. Kick off all users and open the database exclusively to do your work.
3. Usually the best: Create a development environment where you make changes
to the database and test them before putting into production. For this to
work you need to split the database so that you can just swap out the Front
End to the users without losing data in the tables. It really, really helps
if you have figured out your data normalization and tables first so that you
don't have to mess with the back end database much.
Now if you mean doing routine things like adding records and running
reports, that's much simpler.
1. All users of the database must have at least read, write, create, delete
(or modify) privileges to the folder holding the database file. Not just the
database .mdb file, but the entire folder.
2. Open the database and go to Tools, Options, and Advanced Tab. Set the
Default Open mode to Shared and the Default Record Locking to Edited Record.
(While you are in the Options area, go over to the General tab and turn off
Compact on Close and Name AutoCorrect. Trust me on this.)