From the Finder menu, choose 'GO->Computer'
This opens up the available drives on the Mac. Open up your Macintosh hard drive from there.
Now, you will see a folder called 'Users' - go ahead and open it.
Next, choose the name of the user you want to access.
From there, look for a folder called 'Public'
Now, notice the the folder named 'Drop Box' - you won't be able to open it, but you can 'drop' things into it.
Select the file you want to copy and hold down 'OPTION' and 'drag' that file directly 'on' the Drop Box folder.
You Mac might yell at you and tell you that you don't have permission to see the results of this. Ignore it and click 'OK'.
Now to access the file, all the user needs to do is open the drop box folder, which is located in their public folder, which can be found inside of their Home Folder.
If you share files frequently enough, you may consider adding the 'Drop Box' to your sidebar, and then you can just drag and drop files directly onto it.