Multiple Users

How do I allow multiple users to view a .accdb file at the same time?

you do not need to allow it - that is default behaviour

however it is bad practice for multiple users to open the same copy of a datbase file - as it is likely to cause corruption.

the normal method is to split the database, so the processing forms are in one dbs (front-end), and data tables in another (back-end).

each user should then have a separate copy of the processing dbs (front-end), and all of these "point" to the common data dbs. (back-end)