

Mac computers sharing a screen or file share shows up with Mac specific icons. Technically - the PC icon indicates SMB sharing of a printer or file share and/or possibly VNC screen sharing.

Those wouldn't show up if the sharing system preference was turned off for all the potential items to be shared. The rest are Apple computers with file sharing or screen sharing enabled. The PC above is actually a HP printer/scanner that has a slot for a SD card to be read. Yes - you are correct that the preferences just hides those other computers from your view - that computer is still on the network and still "advertising" that it might be sharing files. By default, file sharing is off and if you turn it on, your password and user account is needed on the remote computer to look at any of your shared files. Your Mac controls sharing from the system preferences pane.

If you buy your Mac at an Apple Store, Personal Setup can help you get off to a great start. No - Finder shows you other servers / file shares so think of this like a directory of other computers to knock on their doors to ask if any files are being shared. Built-in Windows-to-Mac migration in macOS automatically transfers your documents, music, contacts, calendars, and email accounts (Outlook and Windows Live Mail), and puts them in the appropriate folders and applications on your new Mac.
