What is Firewall?

A firewall filters network traffic, blocking connections you didn't ask for. Your router's NAT firewall shields the whole home from unsolicited inbound traffic, and each computer runs its own software firewall on top.

Both are on by default and should stay on. If an app can't connect, add a specific exception for it rather than disabling the firewall — an unprotected PC on the open internet is compromised within minutes.