In normal operation, user that have the appropriate rights for a folder ("read") automatically get notifications for each new file. You don't need to do anything.

In case that you have disabled notifiactions in the folder, file or user - you can send out notifications manually by selecting a file in a folder-listing and click "Send Notifications". You can also do this in every file.
Options are: sending to a user, a usergroup, or to everyone (in your userbase).

Folder listing showing the "Send Notifications" menu