LAN USER RESTRICTIONS

communicating HOW? sending you messages?

Unless you have enabled Sharing features {file sharing, screen sharing} all else is private and not accessible from other stations on your network.

System preferences > Sharing

"Sharing" as used in Apple products, means to make available for use by others. There is no reciprocity involved -- others must explicitly allow their things to be "Shared" if that is what they want.

To access the items made available, you simply provide appropriate credentials, similar to login credentials. The shared items will appear in an Icon as if it were an attached drive.

A separate userid used only for sharing makes no sense. It is not created by Apple software automatically.

If you do want to "pass files around" there are some ways to make it easier without compromising security. Your Userid contains a "Public" Folder with relaxed credential requirements, and inside it is a Drop Box, where anyone can drop a file (provided they have access to it. Next to the Users you created, with Home folders in /Users, there is one more that does not have a login, named "Shared".