First, you should split the database into a front-end (containing the
queries, forms, reports, macros and modules), linked to a back-end
(containing the tables and relationships). Only the back-end should be on
the server: each user should have his/her own copy of the front-end. Doing
this significantly reduces the likelihood of database corruption. It also
reduces some network traffic, since it's not necessary to transfer stuff
like form and report definitions across the wire.

Each user needs Read, Write and Create permission on the folder where the
back-end database resides. It's also usual (but not 100% essential) that
each user have Delete permission on that folder. This is because a locking
file (.ldb) gets created in that folder (and no, it's not possible to have
it created somewhere else). The first user to connect to the database causes
the locking file to be created, it's updated by all users connected to the
database, and deleted as the last user disconnects.

Other than that, nothing special needs to be done to use your application.
Access is multiuser enabled out of the box.