What does it mean to trust a network?
When you connect your computer to a network, at least one dialog box should open warning you if you’ve never connected to that network before. If you’re running Windows 7 or later, you should get two separate queries.
The first dialog box to open should be from your firewall program. If it’s doing its job, it should identify that the IP addresses on the network and/or the MAC address of the switch or router to which it is connected, are different than it has seen before.
At that point, it should open a dialog box to warn you that you’re connecting to a new network. That dialog box should also ask you if you want to trust that network. At this point, you should have to respond to the firewall program’s dialog box before the firewall will allow any communications inbound to your computer or outbound from the computer.
With a firewall program, the options are typically Trust the Network or Do Not Trust the Network.
So, what’s the difference?
If you don’t know and trust all the computers and the computer users to have access to your computer, then your answer needs to be that you do not trust that network.
If you trust the network, any files and printers that you have set to be shared can be seen and accessed by those other computers (unless you have set other limiting controls).
Also, if you trust the network, other functions on your computer may be accessible by those other networks — not just file and printer sharing. Some of those functions might be programs that you’re intentionally running on your computer. Others of those functions are programs and services that are run as part of the Windows operating system.
The second dialog box that you’ll get, if you run Windows 7 (and I assume Windows 8), is from Windows itself. It asks the same thing, but in a slightly different manner.
Windows wants you to identify the network as either a Home Network (that you want to trust), a Work Network that you want to trust somewhat, or as a Public Network that you do not want to trust at all.
The Public Network is the appropriate choice when you use a network at a coffee shop, airport, hotel, or similar site.