Access technically doesn't require anything special to make it multi-user. However, to make it stable in a multi-user environment and make it easy to make design changes, best practice is to split the db into FE and BE. The BE (backend) contains ONLY tables. The FE (front end) contains all other objects plus links to the tables in the BE.
The BE is placed in a network folder that is shared by all users of the app. The master copy of the FE is kept in a different server folder and a copy of the FE is distributed to each user and saved on their c: drive.
Do NOT share FE files and do not share unsplit monolithic apps. Both will result in problems and potental corruption that will compromise your data. You also cannot use cloud based services like dropbox to share a BE. Sharing an Access BE can ONLY be done on a LAN. It cannot be done over the internet. There are other options if your users are not on the same LAN so post back if that is your situation.
And finally, don't forget to include the BE in your network back up cycle. Back up at least once per day, more if the app is very active.
There is help available here for making a simple FE distribution method and we're happy to answer other questions also.