Apple has done an excellent job creating a secure multi-user system in OS X. Each local user has their own folder that remains isolated from the rest of the system.
From time to time, you may need to share files between your users. This is accomplished two ways. If you need to share with a single user, you can use the Drop Box. If you want to share files between all of the users you can use the shared folder.
The following video demonstrates how to use the Finder to share files using both methods.