The Drop Box folder earns this name by providing a folder destination that others can copy files to, but without being able to see other files that it may contain. Think of it as being akin to the company Suggestion Box--the padlocked one that has a slot in the top for inserting notes that complain about Margie in Accounting. You can place all the disparaging notes you like in that box, but only the person with the key can view them.
In order for people to copy items into your account's Drop Box, they must first select your Mac from a Finder window's sidebar. The word 'Connecting' will appear at the top-left of the window, and within that window will appear the names of all user accounts on that Mac, followed by 'Public Folder'. So, for example, 'Chris' Public Folder'. Double-click this folder, and you'll find the Drop Box folder within. If you try to open the Drop Box folder, your Mac will inform you that you can't pry it open because you don't have permission to. However, you can drop things into it, at which point they'll be copied to the Mac that hosts the folder.
You can create other folders on your Mac for sharing. To do so, move to the Finder and choose File > New Folder (Shift-Command-N) to create a new folder on the desktop in the window that appears. Select that folder, choose File > Get Info (Command-I), and enable the Shared Folder option. This folder will appear as a shared folder from another Mac on the network.
Simply designating the folder as shared doesn't complete the picture, however. You must also decide what kind of access others should have to the folder.
At the bottom of the Info window that remains open, click the triangle that appears next to Sharing & Permissions. You'll see three listings: your username, 'Staff', and 'Everyone'. Next to your user name will be the words 'Read & Write'. 'Read only' appears next to 'Staff' and 'Everyone'.
With the settings in this configuration, people on other computers can see what's in the folder and can copy items from it to their Macs. They can't, however, add files to the folder. You might set up a folder with these characteristics as a "come-and-get-it" folder where family members or coworkers can go to pick up specific files, without being able to fill the folder with their own stuff. You can change that folder behavior easily enough, if you wish to.
Click the Read Only entry next to Everyone, and you'll see four options: Read & Write, Read Only, Write Only (Drop Box), and No Access. Read & Write permits anyone with such access to take items out of the folder and to put items into it. I've already explained what Read Only does. Write Only describes the behavior of a Drop Box folder: A networked user can place items in it, but can't otherwise access the folder's contents. And No Access means that others don't have permission to access the folder in any way.
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